fill row with previous row from another column

I have a dataframe grouped by Client-Equipment, Date and Closing_Date. I show example:

I need to fill in the Closing dates until the date is equal to the closing date. The expected result would be:

I’m trying codes like this:

df['test'] = df.groupby('Customer-Equipment').apply(
lambda x: x['Closing date'] if x['date'] <= x.at[row.index -1 ,'closing date'] else pd.NaT).fillna(method = 'ffill').reset_index(drop=True)

How could this be done in python?

>Solution :

If your dates are in increasing order, you could just groupby.ffill and mask with where:

s = df.groupby('Customer-Equipment')['Closing Date'].ffill()
df['Closing Date'] = s.where(s.ge(df['Date']))

Output:

        Customer-Equipment        Date Closing Date
0  Customer1 - Equipment A  2023-01-01   2023-01-05
1  Customer1 - Equipment A  2023-01-02   2023-01-05
2  Customer1 - Equipment A  2023-01-03   2023-01-05
3  Customer1 - Equipment A  2023-01-04   2023-01-05
4  Customer1 - Equipment A  2023-01-05   2023-01-05
5  Customer1 - Equipment A  2023-01-06          NaN
6  Customer2 - Equipment H  2023-01-01   2023-01-02
7  Customer2 - Equipment H  2023-01-02   2023-01-02
8  Customer2 - Equipment H  2023-01-03          Nan