• 扁平化 ravel flatten aqueeze reshape(-1) 的区别

squeeze : 将维数为1的删掉

a= np.arange(6.).reshape((2,3))
print(a.squeeze())
print(a)

[[0. 1. 2.]
 [3. 4. 5.]]
[[0. 1. 2.]
 [3. 4. 5.]]

a= np.arange(6.).reshape((6,1))  # 或 reshape((1,6)) 
print(a.squeeze())
print(a)

[0. 1. 2. 3. 4. 5.]
[[0.]
 [1.]
 [2.]
 [3.]
 [4.]
 [5.]]

import numpy as np
a= np.arange(6.).reshape((1,6,1))

print(a.squeeze())

[ 0.  1.  2.  3.  4.  5.]

flatten()返回一份拷贝，对拷贝所做的修改不会影响原始矩阵，而ravel()返回的是视图，会影响原始矩阵。

import numpy as np
a= np.arange(6.).reshape((2,3))

print(a.flatten())
print('\n')

print(a.ravel())

[ 0.  1.  2.  3.  4.  5.]


[ 0.  1.  2.  3.  4.  5.]

• DataFrame中添加一行

import pandas as pd

df = pd.DataFrame({'name':['tom','jack'],'age':[50,18],'sex':['man','woman']})

df.loc[2]=[8,9,6]

print(df)

• ndarray 转 list
  a为ndarray
  b = a.tolist()
  b为列表

• 仅取出特定列

data = pd.read_csv('qq.csv',usecols=['admitted','exam2'])