Pandas 设置值

给选定的位置赋另外的值

import pandas as pd
import numpy as np

dates = pd.date_range('20130101', periods =6)
df = pd.DataFrame(np.arange(24).reshape((6,4)),index=dates,columns = ['A','B','C','D'])
print(df)

             A   B   C   D
2013-01-01   0   1   2   3
2013-01-02   4   5   6   7
2013-01-03   8   9  10  11
2013-01-04  12  13  14  15
2013-01-05  16  17  18  19
2013-01-06  20  21  22  23

按位置或标签修改值

df.iloc[2,2] = 111  # 位置
df.loc['20130101','B'] = 222  # 标签
print(df)

             A    B    C   D
2013-01-01   0  222    2   3
2013-01-02   4    5    6   7
2013-01-03   8    9  111  11
2013-01-04  12   13   14  15
2013-01-05  16   17   18  19
2013-01-06  20   21   22  23

按条件修改值

针对A列>8，修改整个DataFrame

df.A[df.A > 8] = 0 
print(df)

            A    B    C   D
2013-01-01  0  222    2   3
2013-01-02  4    5    6   7
2013-01-03  8    9  111  11
2013-01-04  0    0    0   0
2013-01-05  0    0    0   0
2013-01-06  0    0    0   0

针对A列>8，只修改A列

df.A[df.A > 8] = 0 
print(df)

            A    B    C   D
2013-01-01  0  222    2   3
2013-01-02  4    5    6   7
2013-01-03  8    9  111  11
2013-01-04  0   13   14  15
2013-01-05  0   17   18  19
2013-01-06  0   21   22  23

针对A列>8，修改B列的值

df.B[df.A > 8] = 0 
print(df)

             A    B    C   D
2013-01-01   0  222    2   3
2013-01-02   4    5    6   7
2013-01-03   8    9  111  11
2013-01-04  12    0   14  15
2013-01-05  16    0   18  19
2013-01-06  20    0   22  23

增加列

新增空列

df['F'] = np.nan
print(df)

             A    B    C   D   F
2013-01-01   0  222    2   3 NaN
2013-01-02   4    5    6   7 NaN
2013-01-03   8    9  111  11 NaN
2013-01-04  12    0   14  15 NaN
2013-01-05  16    0   18  19 NaN
2013-01-06  20    0   22  23 NaN

增加其他列，保持index统一

df['E'] = pd.Series(np.arange(1,7),index = df.index)
print(df)

             A    B    C   D   F  E
2013-01-01   0  222    2   3 NaN  1
2013-01-02   4    5    6   7 NaN  2
2013-01-03   8    9  111  11 NaN  3
2013-01-04  12    0   14  15 NaN  4
2013-01-05  16    0   18  19 NaN  5
2013-01-06  20    0   22  23 NaN  6

Pandas学习教程来源请戳这里