How to sum in pandas by unique index in several columns?

Question

I have a pandas DataFrame which details online activities in terms of \"clicks\" during an user session. There are as many as 50,000 unique users, and the dataframe has around 1

Answer 1

The first thing to do is filter registrations dates that precede the registration date, then group on the User_ID and sum.

gb = (df[df.Session >= df.Registration]
      .groupby('User_ID')
      .clicks.agg({'Total_Clicks': np.sum}))

>>> gb
         Total_Clicks
User_ID              
1987293             1
2234214             7
2349876             2
9874452             2

For the use case you mentioned, I believe this is scalable. It always depends, of course, on your available memory.