加速数据分析，这12种高效Numpy和Pandas函数为你保驾护航

知行编程网 2022-05-18 13:00 知行编程网 | 隐藏边栏 | 抢沙发 | 0 0

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选自 | TowardsDataScience

作者 | Kunal Dhariwal

转自 | 机器之心

参与 | Jamin、杜伟、张倩

我们都知道，Numpy 是 Python 环境下的扩展程序库，支持大量的维度数组和矩阵运算；Pandas 也是 Python 环境下的数据操作和分析软件包，以及强大的数据分析库。二者在日常的数据分析中都发挥着重要作用，如果没有 Numpy 和 Pandas 的支持，数据分析将变得异常困难。但有时我们需要加快数据分析的速度，有什么办法可以帮助到我们吗？

在本文中，数据和分析工程师 Kunal Dhariwal 为我们介绍了12 种 Numpy 和 Pandas 函数，这些高效的函数会令数据分析更为容易、便捷。最后，读者也可以在 GitHub 项目中找到本文所用代码的 Jupyter Notebook。

项目地址：https://github.com/kunaldhariwal/12-Amazing-Pandas-NumPy-Functions

Numpy 的 6 种高效函数

首先从 Numpy 开始。Numpy 是用于科学计算的 Python 语言扩展包，通常包含强大的 N 维数组对象、复杂函数、用于整合 C/C++和 Fortran 代码的工具以及有用的线性代数、傅里叶变换和随机数生成能力。

除了上面这些明显的用途，Numpy 还可以用作通用数据的高效多维容器（container），定义任何数据类型。这使得 Numpy 能够实现自身与各种数据库的无缝、快速集成。

接下来一一解析 6 种 Numpy 函数。

argpartition()

借助于 argpartition()，Numpy 可以找出 N 个最大数值的索引，也会将找到的这些索引输出。然后我们根据需要对数值进行排序。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;">x = np.<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">12</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">10</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">12</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">9</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">16</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">4</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>])index_val = np.argpartition(x, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">-4</span>)[<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">-4</span>:]<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />index_val<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>], dtype=int64)np.sort(x[index_val])<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">10</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">12</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">12</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">16</span>])</section>

allclose()

allclose() 用于匹配两个数组，并得到布尔值表示的输出。如果在一个公差范围内（within a tolerance）两个数组不等同，则 allclose() 返回 False。该函数对于检查两个数组是否相似非常有用。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;">array1 = np.array([0.12,0.17,0.24,0.29])<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />array2 = np.array([0.13,0.19,0.26,0.31])<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># with a tolerance of 0.1, it should return False:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />np.allclose(array1,array2,0.1)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />False<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># with a tolerance of 0.2, it should return True:</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />np.allclose(array1,array2,0.2)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />True<span style="color: rgb(51, 51, 51);font-family: mp-quote, -apple-system-font, BlinkMacSystemFont, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei UI", "Microsoft YaHei", Arial, sans-serif;font-size: 17px;text-align: justify;"></span></section>

clip()

Clip() 使得一个数组中的数值保持在一个区间内。有时，我们需要保证数值在上下限范围内。为此，我们可以借助 Numpy 的 clip() 函数实现该目的。给定一个区间，则区间外的数值被剪切至区间上下限（interval edge）。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;">x = np.<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">17</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">14</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">23</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">16</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>])np.clip(x,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>])</section>

extract()

顾名思义，extract() 是在特定条件下从一个数组中提取特定元素。借助于 extract()，我们还可以使用 and 和 or 等条件。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"># Random integers<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span> = np.random.randint(<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">20</span>, size=<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">12</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([ <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">19</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">16</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">18</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">10</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">11</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">13</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">14</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>])#  Divide by <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span> <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">and</span> check <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">if</span> remainder <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">is</span> <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />cond = np.mod(<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>)==<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />cond<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">True</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">True</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">True</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">True</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">False</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">True</span>])# Use extract <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">to</span> <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">get</span> the values<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />np.extract(cond, <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([ <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">19</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">11</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">13</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>])# Apply condition <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">on</span> extract directly<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />np.extract(((<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span> < <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>) | (<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span> > <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">15</span>)), <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([ <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">19</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">16</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">18</span>,  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>])</section>

where()

Where() 用于从一个数组中返回满足特定条件的元素。比如，它会返回满足特定条件的数值的索引位置。Where() 与 SQL 中使用的 where condition 类似，如以下示例所示：

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;">y = np.<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">7</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">9</span>])<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Where y is greater than 5, returns index position</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />np.where(y><span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">2</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">7</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>], dtype=int64),)<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># First will replace the values that match the condition, </span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># second will replace the values that does not</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />np.where(y><span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"Hit"</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"Miss"</span>)<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">array</span>([<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Miss'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Miss'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Hit'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Hit'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Miss'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Hit'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Miss'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Hit'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Hit'</span>],dtype=<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'<U4'</span>)</section>

percentile()

Percentile() 用于计算特定轴方向上数组元素的第 n 个百分位数。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;">a = np.array([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">8</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">7</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6</span>,<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">9</span>])<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">print</span>(<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"50th Percentile of a, axis = 0 : "</span>,  <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />      np.percentile(a, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">50</span>, axis =<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">50</span>th Percentile of a, axis = <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span> :  <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">6.0</span>b = np.array(<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">[[10, 7, 4], [3, 2, 1]]</span>)<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">print</span>(<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"30th Percentile of b, axis = 0 : "</span>,  <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />      np.percentile(b, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">30</span>, axis =<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>))<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">30</span>th Percentile of b, axis = <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span> :  [<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">5.1</span> <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3.5</span> <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1.9</span>]</section>

这就是 Numpy 扩展包的 6 种高效函数，相信会为你带来帮助。接下来看一看 Pandas 数据分析库的 6 种函数。

Pandas 数据统计包的 6 种高效函数

Pandas 也是一个 Python 包，它提供了快速、灵活以及具有显著表达能力的数据结构，旨在使处理结构化 (表格化、多维、异构) 和时间序列数据变得既简单又直观。

Pandas 适用于以下各类数据:

具有异构类型列的表格数据，如 SQL 表或 Excel 表；
有序和无序 (不一定是固定频率) 的时间序列数据；
带有行/列标签的任意矩阵数据（同构类型或者是异构类型）；
其他任意形式的统计数据集。事实上，数据根本不需要标记就可以放入 Pandas 结构中。

Pandas 擅长处理的类型如下所示：

容易处理浮点数据和非浮点数据中的缺失数据（用 NaN 表示）；
大小可调整性: 可以从 DataFrame 或者更高维度的对象中插入或者是删除列；
显式数据可自动对齐: 对象可以显式地对齐至一组标签内，或者用户可以简单地选择忽略标签，使 Series、 DataFrame 等自动对齐数据；
灵活的分组功能，对数据集执行拆分-应用-合并等操作，对数据进行聚合和转换；
简化将数据转换为 DataFrame 对象的过程，而这些数据基本是 Python 和 NumPy 数据结构中不规则、不同索引的数据；
基于标签的智能切片、索引以及面向大型数据集的子设定；
更加直观地合并以及连接数据集；
更加灵活地重塑、转置（pivot）数据集；
轴的分级标记 (可能包含多个标记)；
具有鲁棒性的 IO 工具，用于从平面文件 (CSV 和 delimited)、 Excel 文件、数据库中加在数据，以及从 HDF5 格式中保存 / 加载数据；
时间序列的特定功能: 数据范围的生成以及频率转换、移动窗口统计、数据移动和滞后等。

read_csv(nrows=n)

大多数人都会犯的一个错误是，在不需要.csv 文件的情况下仍会完整地读取它。如果一个未知的.csv 文件有 10GB，那么读取整个.csv 文件将会非常不明智，不仅要占用大量内存，还会花很多时间。我们需要做的只是从.csv 文件中导入几行，之后根据需要继续导入。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;">import io<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />import requests<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># I am using this online data set just to make things easier for you guys</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />url = <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"https://raw.github.com/vincentarelbundock/Rdatasets/master/csv/datasets/AirPassengers.csv"</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />s = requests.get(url).content<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># read only first 10 rows</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />df = pd.read_csv(io.StringIO(s.decode('utf-8')),nrows=10 , index_col=0)</section>

map()

map( ) 函数根据相应的输入来映射 Series 的值。用于将一个 Series 中的每个值替换为另一个值，该值可能来自一个函数、也可能来自于一个 dict 或 Series。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># create a dataframe</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">dframe</span> = pd.DataFrame(np.random.randn(<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">4</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">3</span>), columns=list(<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'bde'</span>), index=[<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'India'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'USA'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'China'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Russia'</span>])<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">#compute a formatted string from each floating point value in frame</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />changefn = lambda x: <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'%.2f'</span> % x<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Make changes element-wise</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />dframe[<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'d'</span>].map(changefn)</section>

apply()

apply() 允许用户传递函数，并将其应用于 Pandas 序列中的每个值。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># max minus mix lambda fn</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />fn = lambda x: x.max() - x.min()<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Apply this on dframe that we've just created above</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />dframe.apply(fn)</section>

isin()

lsin () 用于过滤数据帧。Isin () 有助于选择特定列中具有特定（或多个）值的行。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Using the dataframe we created for read_csv</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(165, 218, 45);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">filter1</span> = df[<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"value"</span>].isin([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">112</span>]) <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(165, 218, 45);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">filter2</span> = df[<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"time"</span>].isin([<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1949.000000</span>])df [filter1 & filter2]</section>

copy()

Copy () 函数用于复制 Pandas 对象。当一个数据帧分配给另一个数据帧时，如果对其中一个数据帧进行更改，另一个数据帧的值也将发生更改。为了防止这类问题，可以使用 copy () 函数。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># creating sample series </span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />data = pd.Series([<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'India'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Pakistan'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'China'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Mongolia'</span>])<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Assigning issue that we face</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />data1= data<br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Change a value</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />data1[<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">0</span>]=<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'USA'</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Also changes value in old dataframe</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />data<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># To prevent that, we use</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># creating copy of series </span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">new</span> = data.copy()<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># assigning new values </span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">new</span>[<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">1</span>]=<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Changed value'</span><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># printing data </span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">print</span>(<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">new</span>) <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">print</span>(data)</section>

select_dtypes()

select_dtypes() 的作用是，基于 dtypes 的列返回数据帧列的一个子集。这个函数的参数可设置为包含所有拥有特定数据类型的列，亦或者设置为排除具有特定数据类型的列。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># We'll use the same dataframe that we used for read_csv</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />framex =  df.select_dtypes(<span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">include</span>=<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"float64"</span>)<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Returns only time column</span></section>

最后，pivot_table( ) 也是 Pandas 中一个非常有用的函数。如果对 pivot_table( ) 在 excel 中的使用有所了解，那么就非常容易上手了。

<section style="box-sizing: border-box;padding: 0.5em;font-size: 14px;color: rgb(169, 183, 198);line-height: 18px;border-radius: 0px;background: rgb(40, 43, 46);display: block;font-family: Consolas, Inconsolata, Courier, monospace;overflow: auto;letter-spacing: 0px;margin-left: 8px;margin-right: 8px;overflow-wrap: normal !important;word-break: normal !important;"><span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Create a sample dataframe</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />school = pd.DataFrame({<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'A'</span>: [<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Jay'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Usher'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Nicky'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Romero'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Will'</span>], <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />      <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'B'</span>: [<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Masters'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Graduate'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Graduate'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Masters'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'Graduate'</span>], <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />      <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'C'</span>: [<span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">26</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">22</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">20</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">23</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(174, 135, 250);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">24</span>]})<span style="box-sizing: border-box;font-size: inherit;color: rgb(128, 128, 128);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"># Lets create a pivot table to segregate students based on age and course</span><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />table = pd.pivot_table(school, <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">values</span> =<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'A'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(248, 35, 117);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">index</span> =[<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'B'</span>, <span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'C'</span>], <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />                         columns =[<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">'B'</span>], aggfunc = np.sum, fill_value=<span style="box-sizing: border-box;font-size: inherit;color: rgb(238, 220, 112);line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;">"Not Available"</span>) <br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  /><br style="box-sizing: border-box;font-size: inherit;color: inherit;line-height: inherit;overflow-wrap: inherit !important;word-break: inherit !important;"  />table</section>

原文链接：

https://towardsdatascience.com/12-amazing-pandas-numpy-functions-22e5671a45b8

<pre style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><p style="padding-right: 0em;padding-left: 0em;max-width: 100%;min-height: 1em;letter-spacing: 0.544px;white-space: normal;color: rgb(0, 0, 0);font-family: -apple-system-font, system-ui, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei UI", "Microsoft YaHei", Arial, sans-serif;widows: 1;line-height: 1.75em;box-sizing: border-box !important;overflow-wrap: break-word !important;"><br  /></p><p style="padding-right: 0em;padding-left: 0em;max-width: 100%;min-height: 1em;letter-spacing: 0.544px;white-space: normal;color: rgb(0, 0, 0);font-family: -apple-system-font, system-ui, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei UI", "Microsoft YaHei", Arial, sans-serif;widows: 1;line-height: 1.75em;box-sizing: border-box !important;overflow-wrap: break-word !important;"><strong style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;letter-spacing: 0.5px;font-size: 14px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><strong style="max-width: 100%;font-size: 16px;letter-spacing: 0.544px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;letter-spacing: 0.5px;box-sizing: border-box !important;overflow-wrap: break-word !important;">—</span></strong>完<strong style="max-width: 100%;font-size: 16px;letter-spacing: 0.544px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;letter-spacing: 0.5px;font-size: 14px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><strong style="max-width: 100%;font-size: 16px;letter-spacing: 0.544px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><span style="max-width: 100%;letter-spacing: 0.5px;box-sizing: border-box !important;overflow-wrap: break-word !important;">—</span></strong></span></strong></span></strong></p><section style="padding-right: 0em;padding-left: 0em;max-width: 100%;letter-spacing: 0.544px;white-space: normal;font-family: -apple-system-font, system-ui, "Helvetica Neue", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei UI", "Microsoft YaHei", Arial, sans-serif;widows: 1;box-sizing: border-box !important;overflow-wrap: break-word !important;"><section powered-by="xiumi.us" style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><section style="margin-top: 15px;margin-bottom: 25px;max-width: 100%;opacity: 0.8;box-sizing: border-box !important;overflow-wrap: break-word !important;"><section style="max-width: 100%;box-sizing: border-box !important;overflow-wrap: break-word !important;"><section style="max-width: 100%;letter-spacing: 0.544px;box-sizing: border-box !important;overflow-wrap: break-word !important;"><section powered-by="xiumi.us" style="max-width: 100%;box-sizing: 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