use strict; use warnings; use List::Util qw{sum min max}; my %data; while () { chomp; my ($id, $value) = split /,/; push @{ $data{$id} }, $value; # store values as HoA } for my $id (sort keys %data) { print "$id: " . summarise($data{$id}); } sub summarise{ my $arr = shift; return "max=" . max( @$arr ) . " min=" . min( @$arr ) . " sum=" . sum( @$arr ) . " mean=" . ( sum( @$arr )/scalar@$arr ) . "\n"; } __DATA__ A,10 A,11 A,12 A,13 B,15 B,16 C,17 D,18 #### A: max=13 min=10 sum=46 mean=11.5 B: max=16 min=15 sum=31 mean=15.5 C: max=17 min=17 sum=17 mean=17 D: max=18 min=18 sum=18 mean=18