Pandas条件创建Series/DataFrame列

Question

    Type       Set
1    A          Z
2    B          Z           
3    B          X
4    C          Y

做这件事最好的方法是什么？

Answer 1

如果您只有两个选择可供选择：

df['color'] = np.where(df['Set']=='Z', 'green', 'red')

例如,

import pandas as pd
import numpy as np

df = pd.DataFrame({'Type':list('ABBC'), 'Set':list('ZZXY')})
df['color'] = np.where(df['Set']=='Z', 'green', 'red')
print(df)

收益率

  Set Type  color
0   Z    A  green
1   Z    B  green
2   X    B    red
3   Y    C    red

null

df = pd.DataFrame({'Type':list('ABBC'), 'Set':list('ZZXY')})
conditions = [
    (df['Set'] == 'Z') & (df['Type'] == 'A'),
    (df['Set'] == 'Z') & (df['Type'] == 'B'),
    (df['Type'] == 'B')]
choices = ['yellow', 'blue', 'purple']
df['color'] = np.select(conditions, choices, default='black')
print(df)

  Set Type   color
0   Z    A  yellow
1   Z    B    blue
2   X    B  purple
3   Y    C   black