#!/usr/bin/perl -w
use strict;
my %seen = ();
while (<DATA>) {
	my ($one, $two) = split;
	$seen{$one} = [$two, exists $seen{$one} ? @{$seen{$one}} : () ];
}
for my $key (keys %seen) {
	print $key, " ", join(", ", @{$seen{$key}}), "\n";
}
__DATA__
a 1
a 2
a 3
a 4
b 1
c 1
d 1