简约而不简单！值得收藏的 NumPy 小抄表（含主要语法、代码）

知行编程网 2022-06-13 16:00 知行编程网 | 隐藏边栏 | 抢沙发 | 5 0

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Numpy是一个用python实现的科学计算的扩展程序库，包括：

1、一个强大的N维数组对象Array；
2、比较成熟的（广播）函数库；
3、用于整合C/C++和Fortran代码的工具包；
4、实用的线性代数、傅里叶变换和随机数生成函数。numpy和稀疏矩阵运算包scipy配合使用更加方便。

NumPy（Numeric Python）提供了许多高级的数值编程工具，如：矩阵数据类型、矢量处理，以及精密的运算库。专为进行严格的数字处理而产生。多为很多大型金融公司使用，以及核心的科学计算组织如：Lawrence Livermore，NASA用其处理一些本来使用C++，Fortran或Matlab等所做的任务。

本文整理了一个Numpy的小抄表，总结了Numpy的常用操作，可以收藏慢慢看。

安装Numpy

可以通过 Pip 或者 Anaconda安装Numpy:

或

本文目录

基础
数组
数学计算
切片和子集
小技巧

基础

NumPy最常用的功能之一就是NumPy数组：列表和NumPy数组的最主要区别在于功能性和速度。

列表提供基本操作，但NumPy添加了FTTs、卷积、快速搜索、基本统计、线性代数、直方图等。

两者数据科学最重要的区别是能够用NumPy数组进行元素级计算。

<span style="font-size: 16px;">axis 0</span> 通常指行

axis 1 通常指列

操作	描述	文档
`<span style="font-size: 14px;">np.array([1,2,3])</span>`	一维数组	https://numpy.org/doc/stable/reference/generated/numpy.array.html#numpy.array
`<span style="font-size: 14px;">np.array([(1,2,3),(4,5,6)])</span>`	二维数组	https://numpy.org/doc/stable/reference/generated/numpy.array.html#numpy.array
`<span style="font-size: 14px;">np.arange(start,stop,step)</span>`	等差数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.arange.html

占位符

操作	描述	文档
`<span style="font-size: 14px;">np.linspace(0,2,9)</span>`	数组中添加等差的值	https://docs.scipy.org/doc/numpy/reference/generated/numpy.linspace.html
`<span style="font-size: 14px;">np.zeros((1,2))</span>`	创建全0数组	docs.scipy.org/doc/numpy/reference/generated/numpy.zeros.html
`<span style="font-size: 14px;">np.ones((1,2))</span>`	创建全1数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.ones.html#numpy.ones
`<span style="font-size: 14px;">np.random.random((5,5))</span>`	创建随机数的数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.random.random.html
`<span style="font-size: 14px;">np.empty((2,2))</span>`	创建空数组	https://numpy.org/doc/stable/reference/generated/numpy.empty.html

举例：

数组

数组属性

语法	描述	文档
`<span style="font-size: 14px;">array.shape</span>`	维度(行,列)	https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.shape.html
`<span style="font-size: 14px;">len(array)</span>`	数组长度	https://docs.python.org/3.5/library/functions.html#len
`<span style="font-size: 14px;">array.ndim</span>`	数组的维度数	https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.ndim.html
`<span style="font-size: 14px;">array.size</span>`	数组的元素数	https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.size.html
`<span style="font-size: 14px;">array.dtype</span>`	数据类型	https://docs.scipy.org/doc/numpy/reference/arrays.dtypes.html
`<span style="font-size: 14px;">array.astype(type)</span>`	转换数组类型	https://docs.scipy.org/doc/numpy/reference/generated/numpy.ndarray.astype.html
`<span style="font-size: 14px;">type(array)</span>`	显示数组类型	https://numpy.org/doc/stable/user/basics.types.html

拷贝 /排序

操作	描述	文档
`<span style="font-size: 14px;">np.copy(array)</span>`	创建数组拷贝	https://docs.scipy.org/doc/numpy/reference/generated/numpy.copy.html
`<span style="font-size: 14px;">other = array.copy()</span>`	创建数组深拷贝	https://docs.scipy.org/doc/numpy/reference/generated/numpy.copy.html
`<span style="font-size: 14px;">array.sort()</span>`	排序一个数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.sort.html
`<span style="font-size: 14px;">array.sort(axis=0)</span>`	按照指定轴排序一个数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.sort.html

举例

数组操作例程

增加或减少元素

操作	描述	文档
`<span style="font-size: 14px;">np.append(a,b)</span>`	增加数据项到数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.append.html
`<span style="font-size: 14px;">np.insert(array, 1, 2, axis)</span>`	沿着数组0轴或者1轴插入数据项	https://docs.scipy.org/doc/numpy/reference/generated/numpy.insert.html
`<span style="font-size: 14px;">np.resize((2,4))</span>`	将数组调整为形状(2,4)	https://docs.scipy.org/doc/numpy/reference/generated/numpy.resize.html
`<span style="font-size: 14px;">np.delete(array,1,axis)</span>`	从数组里删除数据项	https://numpy.org/doc/stable/reference/generated/numpy.delete.html

举例

组合数组

操作	描述	文档
`<span style="font-size: 14px;">np.concatenate((a,b),axis=0)</span>`	连接2个数组，添加到末尾	https://docs.scipy.org/doc/numpy/reference/generated/numpy.concatenate.html
`<span style="font-size: 14px;">np.vstack((a,b))</span>`	按照行堆叠数组	https://numpy.org/doc/stable/reference/generated/numpy.vstack.html
`<span style="font-size: 14px;">np.hstack((a,b))</span>`	按照列堆叠数组	docs.scipy.org/doc/numpy/reference/generated/numpy.hstack.html#numpy.hstack

举例

分割数组

操作	描述	文档
`<span style="font-size: 14px;">numpy.split()</span>`	分割数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.split.html
`<span style="font-size: 14px;">np.array_split(array, 3)</span>`	将数组拆分为大小（几乎）相同的子数组	https://docs.scipy.org/doc/numpy/reference/generated/numpy.array_split.html#numpy.array_split
`<span style="font-size: 14px;">numpy.hsplit(array, 3)</span>`	在第3个索引处水平拆分数组	https://numpy.org/doc/stable/reference/generated/numpy.hsplit.html#numpy.hsplit

举例

数组形状变化

操作	描述	文档
`<span style="font-size: 14px;">other = ndarray.flatten()</span>`	平铺一个二维数组到一维数组	https://numpy.org/doc/stable/reference/generated/numpy.ndarray.flatten.html
numpy.flip()	翻转一维数组中元素的顺序	https://docs.scipy.org/doc/stable/reference/generated/numpy.flip.html
np.ndarray[::-1]	翻转一维数组中元素的顺序
reshape	改变数组的维数	https://docs.scipy.org/doc/stable/reference/generated/numpy.reshape.html
squeeze	从数组的形状中删除单维度条目	https://numpy.org/doc/stable/reference/generated/numpy.squeeze.html
expand_dims	扩展数组维度	https://docs.scipy.org/doc/numpy-1.13.0/reference/generated/numpy.expand_dims.html

其他

操作	描述	文档
`<span style="font-size: 14px;">other = ndarray.flatten()</span>`	平铺2维数组到1维数组	https://numpy.org/doc/stable/reference/generated/numpy.ndarray.flatten.html
`<span style="font-size: 14px;">array = np.transpose(other)</span>` `<span style="font-size: 14px;">array.T</span>`	数组转置	https://numpy.org/doc/stable/reference/generated/numpy.transpose.html
`<span style="font-size: 14px;">inverse = np.linalg.inv(matrix)</span>`	求矩阵的逆矩阵	https://docs.scipy.org/doc/numpy/reference/generated/numpy.linalg.inv.html

举例

数学计算

操作

操作	描述	文档
`<span style="font-size: 14px;">np.add(x,y)</span>` `<span style="font-size: 14px;">x + y</span>`	加	https://docs.scipy.org/doc/numpy/reference/generated/numpy.add.html
`<span style="font-size: 14px;">np.substract(x,y)</span>` `<span style="font-size: 14px;">x - y</span>`	减	https://docs.scipy.org/doc/numpy/reference/generated/numpy.subtract.html#numpy.subtract
`<span style="font-size: 14px;">np.divide(x,y)</span>` `<span style="font-size: 14px;">x / y</span>`	除	https://docs.scipy.org/doc/numpy/reference/generated/numpy.divide.html#numpy.divide
`<span style="font-size: 14px;">np.multiply(x,y)</span>` `<span style="font-size: 14px;">x * y</span>`	乘	https://docs.scipy.org/doc/numpy/reference/generated/numpy.multiply.html#numpy.multiply
`<span style="font-size: 14px;">np.sqrt(x)</span>`	平方根	https://docs.scipy.org/doc/numpy/reference/generated/numpy.sqrt.html#numpy.sqrt
`<span style="font-size: 14px;">np.sin(x)</span>`	元素正弦	https://docs.scipy.org/doc/numpy/reference/generated/numpy.sin.html#numpy.sin
`<span style="font-size: 14px;">np.cos(x)</span>`	元素余弦	https://docs.scipy.org/doc/numpy/reference/generated/numpy.cos.html#numpy.cos
`<span style="font-size: 14px;">np.log(x)</span>`	元素自然对数	https://docs.scipy.org/doc/numpy/reference/generated/numpy.log.html#numpy.log
`<span style="font-size: 14px;">np.dot(x,y)</span>`	点积	https://docs.scipy.org/doc/numpy/reference/generated/numpy.dot.html
`<span style="font-size: 14px;">np.roots([1,0,-4])</span>`	给定多项式系数的根	https://docs.scipy.org/doc/numpy/reference/generated/numpy.roots.html

举例

比较

操作	描述	文档
`<span style="font-size: 14px;">==</span>`	等于	https://docs.python.org/2/library/stdtypes.html
`<span style="font-size: 14px;">!=</span>`	不等于	https://docs.python.org/2/library/stdtypes.html
`<span style="font-size: 14px;"><</span>`	小于	https://docs.python.org/2/library/stdtypes.html
`<span style="font-size: 14px;">></span>`	大于	https://docs.python.org/2/library/stdtypes.html
`<span style="font-size: 14px;"><=</span>`	小于等于	https://docs.python.org/2/library/stdtypes.html
`<span style="font-size: 14px;">>=</span>`	大于等于	https://docs.python.org/2/library/stdtypes.html
`<span style="font-size: 14px;">np.array_equal(x,y)</span>`	数组比较	https://numpy.org/doc/stable/reference/generated/numpy.array_equal.html

举例：

基本的统计

操作	描述	文档
`<span style="font-size: 14px;">np.mean(array)</span>`	Mean	https://numpy.org/doc/stable/reference/generated/numpy.mean.html#numpy.mean
`<span style="font-size: 14px;">np.median(array)</span>`	Median	https://numpy.org/doc/stable/reference/generated/numpy.median.html#numpy.median
`<span style="font-size: 14px;">array.corrcoef()</span>`	Correlation Coefficient	https://numpy.org/doc/stable/reference/generated/numpy.corrcoef.html#numpy.corrcoef
`<span style="font-size: 14px;">np.std(array)</span>`	Standard Deviation	https://docs.scipy.org/doc/numpy/reference/generated/numpy.std.html#numpy.std

举例

操作	描述	文档
`<span style="font-size: 14px;">array.sum()</span>`	数组求和	https://numpy.org/doc/stable/reference/generated/numpy.sum.html
`<span style="font-size: 14px;">array.min()</span>`	数组求最小值	https://numpy.org/doc/stable/reference/generated/numpy.ndarray.min.html
`<span style="font-size: 14px;">array.max(axis=0)</span>`	数组求最大值（沿着0轴）
`<span style="font-size: 14px;">array.cumsum(axis=0)</span>`	指定轴求累计和	https://numpy.org/doc/stable/reference/generated/numpy.cumsum.html

切片和子集

操作	描述	文档
`<span style="font-size: 14px;">array[i]</span>`	索引i处的一维数组	https://numpy.org/doc/stable/reference/arrays.indexing.html
`<span style="font-size: 14px;">array[i,j]</span>`	索引在[i][j]处的二维数组	https://numpy.org/doc/stable/reference/arrays.indexing.html
`<span style="font-size: 14px;">array[i<4]</span>`	布尔索引	https://numpy.org/doc/stable/reference/arrays.indexing.html
`<span style="font-size: 14px;">array[0:3]</span>`	选择索引为 0, 1和 2	https://numpy.org/doc/stable/reference/arrays.indexing.html
`<span style="font-size: 14px;">array[0:2,1]</span>`	选择第0,1行，第1列	https://numpy.org/doc/stable/reference/arrays.indexing.html
`<span style="font-size: 14px;">array[:1]</span>`	选择第0行数据项 (与[0:1, :]相同)	https://numpy.org/doc/stable/reference/arrays.indexing.html
`<span style="font-size: 14px;">array[1:2, :]</span>`	选择第1行	https://numpy.org/doc/stable/reference/arrays.indexing.html
[comment]: <> "	`<span style="font-size: 14px;">array[1,...]</span>`	等同于 array[1,:,:]
`<span style="font-size: 14px;">array[ : :-1]</span>`	反转数组	同上

举例

切片举例

生成矩阵和切片图示

小技巧

例子将会越来越多的，欢迎大家提交。

布尔索引

【参考】

https://github.com/juliangaal/python-cheat-sheet

—完—

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