Python数据分析：numpy

numpy创建数组(矩阵)

创建数组

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="python3" cid="n234" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">import numpy as np
a = np.array([1, 2, 3, 4, 5])
b = np.array(range(1, 6))
c = np.arange(1, 6)  # np.arange用法：arange(start,stop,step,dtype=None)</pre>

数组的类名和数据的类型

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n236" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">In [1]: type（a）
Out[1]: numpy.ndarray
In [2]: a.dtype
Out[2]: dtype('int64') # 常见类型有int,uint(8,16,32,64),float(16,32,64,128),complex(64,128,256),bool</pre>

数据类型的操作

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n238" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a = np.array([1,0,1,0], dtype=np.bool) # 创建数组时指定数据类型
a.astype(np.int8)  # 修改数组的数据类型
b = np.array([0.0485,0.2689,1.8567,0.8754])
np.round(b, 2)  # 修改浮点型小数位数</pre>

数组的形状

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n240" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a.shape  # 查看数组形状
a.reshape(2,2) # 修改数组形状
a.flatten（）  # 把多维数组转化为一维数组</pre>

数组的计算

数组和数的计算

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n243" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a = np.array([1, 2, 3, 4, 5])
b = a + 1  # 按位相加
c = a * 3  # 按位相乘</pre>

数组与数组的计算

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n245" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a = np.array([[1, 2, 3, 4],
 [5, 6, 7, 8]])
b = np.array([[1, 1, 1, 1],
 [1, 1, 1, 1]])
c = np.array([1, 1, 1, 1])
d = np.array([[1],
 [1]])
O1 = a + b  # 形状相同按位相加
O2 = a + c
O3 = a + d  # 形状不同，只有满足广播原则才可计算，O1=O2=O3</pre>

数组的转置

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n247" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a.transpose()
a.swapaxes(1,0)
a.T</pre>

以上的三种方法都可以实现二维数组的转置的效果，转置和交换轴的效果一样。

## numpy索引和切片

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="text" cid="n250" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a[1,:]  # 取一行，可简写为a[1] 
a[:,2]  # 取一列
a[1:3,:]  # 取连续多行，可简写为a[1：3] 
a[:,2:4]  # 取连续多列
a[[1,3],:]  # 取离散多行，可简写为a[[1,3]]
a[:,[2,4]]  # 取离散多行
a[a<2]  # bool索引
np.where(a<2,0,4)  # 三元运算符,满足条件1替换为0，不满足替换为4
a.clip(2,3)  # 裁剪，大于3替换为3，小于2替换为2</pre>

numpy中的nan和inf

> nan(NAN,Nan):not a number，表示不是一个数字，type类型为float。（两个nan是不相等的）  inf:infinity，inf表示正无穷，-inf表示负无穷，type类型为float

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="python3" cid="n254" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">np.count_nonzero(a!=a)  # 判断a中nan个数
np.isnan(a)  # 判断是否为nan，返回bool类型
a[np.isnan(a)] = 0 # nan 替换为0</pre>

numpy中常用统计函数

求和：t.sum(axis=None)

均值：t.mean(axis=None)

中值：np.median(t,axis=None)

最大值：t.max(axis=None)

最小值：t.min(axis=None)

极值：np.ptp(t,axis=None) 即最大值和最小值之差

标准差：t.std(axis=None)

默认返回多维数组的全部的统计结果,如果指定axis则返回一个当前轴上的结果

数组的拼接

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="python3" cid="n265" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">np.vstack(a,b) # 竖直拼接
np.hstack(a,b) # 水平拼接</pre>

数组的行列交换

<pre spellcheck="false" class="md-fences md-end-block ty-contain-cm modeLoaded" lang="python3" cid="n267" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">a[[1,2],:] = a[[2,1],:] # 行交换
a[:,[0,2]] = a[:,[2,0]] # 列交换</pre>

其他实用方法

1.获取最大值最小值的位置

np.argmax(t,axis=0)

np.argmin(t,axis=1)

2.创建一个全0的数组: np.zeros((3,4))

3.创建一个全1的数组:np.ones((3,4))

4.创建一个对角线为1的正方形数组(方阵)：np.eye(3)

5.numpy生成随机数

![image](https://upload-images.jianshu.io/upload_images/27489505-62d03da0a9854236.jpg?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)

注意：numpy的copy和view

a=b 完全不复制，a和b相互影响
a = b[:],视图的操作，一种切片，会创建新的对象a，但是a的数据完全由b保管，他们两个的数据变化是一致的，
a = b.copy(),复制，a和b互不影响

本次分享就到这啦，如果对您有帮助的话，麻烦点个关注再走哦~