python - Replace() 没有找到日期，也没有转换为另一个字符串

Question

我在 csv 中有一个数组:

    date        group
0   2015-01-02  WODKA
1   2015-01-02  PIWO
2   2015-01-02  2015-01-02
3   2015-01-03  WODKA
4   2015-01-03  PIWO
5   2015-01-03  2015-01-03
6   2015-01-03  WODKA
7   2015-01-03  PIWO

我想将“group”列中的所有日期转换为“sum”一词。但是我的代码不起作用...

import pandas as pd
import numpy as np
from datetime import datetime as dt

x = pd.read_csv("C:\\Users\dell\\Desktop\\list_1.csv", sep=';')
x.group = x.group.replace(dt, 'sum')

Answer 1

我们可以更新那些可以将 group 转换为 datetime 的行:

In [40]: df.loc[pd.to_datetime(df['group'], errors='coerce').notnull(), 'group'] = 'sum'

In [41]: df
Out[41]:
         date  group
0  2015-01-02  WODKA
1  2015-01-02   PIWO
2  2015-01-02    sum
3  2015-01-03  WODKA
4  2015-01-03   PIWO
5  2015-01-03    sum
6  2015-01-03  WODKA
7  2015-01-03   PIWO

或使用 RegEx(注意:第一个解决方案更加灵活，因为它支持不同的日期格式):

In [46]: df['sum'] = df['group'].str.replace(r'^\d{4}-\d{2}-\d{2}', 'sum')

In [47]: df
Out[47]:
         date       group    sum
0  2015-01-02       WODKA  WODKA
1  2015-01-02        PIWO   PIWO
2  2015-01-02  2015-01-02    sum
3  2015-01-03       WODKA  WODKA
4  2015-01-03        PIWO   PIWO
5  2015-01-03  2015-01-03    sum
6  2015-01-03       WODKA  WODKA
7  2015-01-03        PIWO   PIWO