See Re: Perl File Column Comparison. and Re: Need to extract first n rows and parsing multiple files and hash to count occurences, they both links examples of reading csv ....

so copy/paste that part, then accumulate whatever sums and counts you need in a hash, say  $foo{ $id } += $val ...

Then , after you're done reading processing accumulating in a hash, you've got a hash of number, apply your statistics functions and print the info

Good luck