比较在i上有文本的两个日期列

Question

我有这样一个数据帧

datecol1              datecol2
2005-02-22          EmployeeNotFound
2010-02-21          2010-02-22
EmployeeNotFound    EmployeeNotFound
EmployeeNotFound    2010-02-22

两列的数据类型都是Object

我想比较这两列并得到每列的最大日期

所以预期的结果是

    datecol1            datecol2                  ExpectedResult
    2005-02-22          EmployeeNotFound          2005-02-22
    2010-02-21          2010-02-22                2010-02-22
    EmployeeNotFound    EmployeeNotFound          EmployeeNotFound
    EmployeeNotFound    2010-02-25                2010-02-25

ExpectedResult的数据类型将再次成为对象

Answer 1

也可以使用numpy，因为numpy函数更快

import numpy as np
cond = df['datecol1'] != 'EmployeeNotFound'
df['ExpectedResult'] = np.where(cond, df['datecol1'], df['datecol2'])

这里首先将填充datecol1的所有有效值，然后剩余的值将由第二列datecol2填充