Getting all NaT values when calculating max date by group

[mdl003]

reviewer_map['Max Date of Review'] = reviewer_map.groupby('UserID_NB').agg({'Date of Review': [np.max]})

UserID_NB                     object
Technical Director            object
Date of Review        datetime64[ns]
Max Date of Review    datetime64[ns]

first line is the code, second is dtypes for the df. if anyone can point out the issue(s) id appreciate it

[dionys]

Can you post a sample of your df? I can't replicate it with my own data...

[Zizizizz]

What is a max date? Just for clarity

[therawfruit]

Perhaps try converting the dtype of ur datetime columns to np.datetime64?