I'd stash everything into a data structure (HoHoA, ie. hash of hashes of arrays), which makes sure everything gets aggregated properly, then print it out.

use warnings;
use strict;

my %hash;

while (<DATA>){
    chomp;
    my ($key, $val, $colour) = split;
    push @{ $hash{$key}{$val} }, $colour;
}

for my $k (keys %hash){
    for (keys %{ $hash{$k} }){
        my $colours = join ':', @{ $hash{$k}{$_} };
        print "$k $_ $colours\n";
    }
}

__DATA__
A1 abc yellow
B1 xyz green
A2 cde red
A1 abc green
A2 cde yellow
A1 abc blue

[download]

Output:

A1 abc yellow:green:blue
A2 cde red:yellow
B1 xyz green

[download]

In reply to Re: join column 3 for unique values by stevieb
in thread join column 3 for unique values by hello_beginner

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