Convert a binary dataframe to a grouped (long) list of combinations

I have the following binary dataframe

A    B    C    D  0    1    1    0  0    0    1    1  1    1    1    0  0    1    1    1  

I would like to create a list with all the column combinations and count the rows with '1' that are in common.

More precisely something like that:

A    B    1  A    C    1  A    D    0  B    A    1  B    C    3  B    D    1  C    A    1  C    B    3  C    D    2  D    A    0  D    B    1  D    C    2  

But I'm struggling to think of a way to do that in R. I would appreciate any hint towards the right direction

Alternatively, a 'correlation'-like matrix would work for me. For example:

    A    B    C    D  A   0    1    1    0  B   1    0    3    1  C   1    3    0    2  D   0    1    2    0     

https://stackoverflow.com/questions/66078607/convert-a-binary-dataframe-to-a-grouped-long-list-of-combinations February 06, 2021 at 11:33PM