Spring batch : reading a csv file and modify this list before putting the results in another file

i have a csv file i retreive i retrieve all of these lines and I put these lines in another csv file.

I need to make a change on this list. For example group all the lines which have the same type in a single line and the sum of an integer type column for example.

can someone help me ? I lost a lot of time to realize this little spot.

Thanks.

EDIT

A small example to explain.

I want to achieve something like this

The input file :

A 1

A 2

B 1

B 3

the output file should be like this

A 3 ( 1+2 )

B 4 ( 1+3 )