id1    name1 cat1  catname1
id1    name1 cat2  catname2
id2    name2 cat3  catname3
id3    name3 cat1  catname1
id3    name3 cat4  catname4

##</code><code>##

id1    name1 cat1:catname1, cat2:catname2
id2    name2 cat3:catname3
id3    name3 cat1:catname1, cat4:catname4

##</code><code>##

my @val = split(" ",$val);
my $v = join (":", @val);

##</code><code>##

if (exists $hash{$key}) {
	$hash{$key} .= $sep.$v;
}
else {
	$hash{$key} = $v;
}

##</code><code>##

#!/usr/bin/perl

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

my %hash;
my $sep = ", ";

while (<DATA>) {
	chomp;
	(my $key, my $val) = /(\S*\s*\S*\s*)(\S*\s*\S*\s*)/;
	my @val = split(" ",$val);
	my $v = join (":", @val);
	if (exists $hash{$key}) {
		$hash{$key} .= $sep.$v;
	}
	else {
		$hash{$key} = $v;
	}
}

foreach my $k (sort keys %hash) {
    print $k.$hash{$k}."\n";
}

#print Dumper \%h;

__DATA__
id1    name1 cat1  catname1
id1    name1 cat2  catname2
id2    name2 cat3  catname3
id3    name3 cat1  catname1
id3    name3 cat4  catname4