检查数据框中的多个字段（字符串字段和日期字段）

Question

I have a dataframe ( df ) that looks like:

Id                  Status  Date of entry to current post  Date of entry to current payband
 1  NEW ENTRANT - EXTERNAL                       1/1/2020                         1/1/2019
 2                 CURRENT                       1/1/2020                         1/1/2020 

I am trying to write a validation that returns any records that have a Date of entry to current post that is before Date of entry to current payband and the Status field is a new entrant type (there are a few hence the wildcard).

I have tried the following without success

df['Date of entry to current post']>df['Date of entry to current payband'] & df['Status'] =='NEW ENTRANT*')

So in this example I would like returned:

Id                  Status  Date of entry to current post  Date of entry to current payband
 1  NEW ENTRANT - EXTERNAL                       1/1/2020                         1/1/2019

How can I tackle this?

Answer 1

If you have datetime columns for your dates, this should work:

import numpy as np
df['Condition'] = np.where((df['Date of entry to current post']>df['Date of entry to current payband']) & (df['Status'] =='NEW ENTRANT*'), 1, 0)
df = df.loc[df['Condition'] == 1)

Answer 2

You are comparing to the string 'NEW ENTRANT*' meaning a string actually containing the * character.

What you want is:

... & df['Status'].str.match('NEW ENTRANT'))

But if the date columns actually contain strings, you will compare them in lexicographic order which is probably not what you want...