How to use java streams: Is it possible to create your own Map within the stream intermediate operation?

- how to use java stream to get the result*

Function, Map> countTotalByCategory = ?

I have stream from a file like this:

A,B,C,2,3,4

A,_,C1,2,3

A,B,_,1,1,1

The map should look like:

*result:

A =3 [because 3+2+1]

B=6 [3+2+1]

C=8