use warnings;
use strict;
use Data::Dumper;

my @arr = (
    [12, "abc", 30],
    [24, "abc", 30],
    [26, "abc", 30],
    [14, "abc", 40],
    [46, "abc", 40],
    [2,  "abc", 50]
);

my %res;

map { push @{$res{$_->[2]}}, $_ } @arr;

warn Dumper values %res;