Datetime and ID Based Cumcount Pandas

Question

I'm trying to achieve a cumulative count in a Pandas column that's a little tricky, where it only adds a count ONCE per date and ID number.

The visual below will help explain, my current dataset looks like this:

ID     Date     Mention_of_Yes
XDA  11/19/2019     0
XDA  12/19/2019     1
XDA  12/19/2019     1
XDA  1/19/2020      1
XDA  2/19/2020      0
XDA  3/19/2020      1
JJL  11/2/2019      1
JJL  11/2/2019      1
JJL  12/2/20019     0
JJL  1/20/2020      1

And I'm attempting to add a column thats counts in this specific way, only ONCE per "Mention's of Yes" on a specific date:

ID    Date      Mention_of_Yes    *Correct CumCount 
XDA  11/19/2019      0                     0    
XDA  12/19/2019      1                     1    
XDA  12/19/2019      1                     1** Only Counts Once Per Date (12/19/2019 in this case)
XDA  1/19/2020       1                     2    
XDA  2/19/2020       0                     2    
XDA  3/19/2020       1                     3
JJL  19/2/2019       0                     0
JJL  10/2/2019       0                     0    
JJL  11/2/2019       1                     1    
JJL  11/2/2019       1                     1** Only Counts Once Per Date (11/2/2019 in this case)
JJL  12/2/20019      0                     1    
JJL  1/20/2020       1                     2    

I've tried different iterations of groupby and cumcount, but can't seem to get the configuration right, like with the code I've used below:

df['Correct_CumCount'] = df.groupby[('ID','Mention_of_Yes')].cumcount()+1

Any help would be greatly appreciated!

Answer 1

you can do it with groupby and cumsum (not cumcount ) after drop_duplicates , then ffill like:

df['Correct_CumCount'] = df.drop_duplicates(subset=['ID', 'Date', 'Mention_of_Yes'], 
                                            keep='first')\
                           .groupby('ID')['Mention_of_Yes'].cumsum()
df['Correct_CumCount'] = df['Correct_CumCount'].ffill().astype(int)

print (df)
    ID        Date  Mention_of_Yes  Correct_CumCount
0  XDA  11/19/2019               0                 0
1  XDA  12/19/2019               1                 1
2  XDA  12/19/2019               1                 1
3  XDA   1/19/2020               1                 2
4  XDA   2/19/2020               0                 2
5  XDA   3/19/2020               1                 3
6  JJL   11/2/2019               1                 1
7  JJL   11/2/2019               1                 1
8  JJL  12/2/20019               0                 1
9  JJL   1/20/2020               1                 2