indexing - Find indices of a groupby in pandas

Question

I have this fake dataset:

And I want to find how many times a combination of BirthDate and ZipCode occur, like so:

Now, my question is how can I find the positions in the dataset df where these occurences happen? For example, how can I find the position where 2000101 and 08002 are?

Thanks in advance.

question from:https://stackoverflow.com/questions/66061685/find-indices-of-a-groupby-in-pandas

Answer 1

Use GroupBy.agg if need aggregate for counts and for index values like list to new column Pos:

df1 = (df.reset_index()
         .groupby(['BithDate','ZipCode'])
         .agg(RowNumber=('BithDate','size'), Pos = ('index',list)))