DataFrame利用函数或映射进行数据转换map

from pandas import DataFrame,Series
import pandas as pd
import numpy as np

data = DataFrame({'k1':['A']*3+['B']*4,
                  'k2':[1,1,2,3,3,4,4]})
print(data)
'''
  k1  k2
0  A   1
1  A   1
2  A   2
3  B   3
4  B   3
5  B   4
6  B   4
'''
# 编写一个映射
a_to_b = {
    'A':'ONE',
    'B':'TWO',
    'C':'THREE'
}

data['k3'] = data['k1'].map(a_to_b)
print(data)
'''
  k1  k2   k3
0  A   1  ONE
1  A   1  ONE
2  A   2  ONE
3  B   3  TWO
4  B   3  TWO
5  B   4  TWO
6  B   4  TWO
'''
data['k4'] = data['k1'].map(lambda x:a_to_b[x])
print(data)
'''
  k1  k2   k3   k4
0  A   1  ONE  ONE
1  A   1  ONE  ONE
2  A   2  ONE  ONE
3  B   3  TWO  TWO
4  B   3  TWO  TWO
5  B   4  TWO  TWO
6  B   4  TWO  TWO
'''