A1 text1  NY   Jan  01
A2 text2  LN   Feb  02
A3 text3  SG   Mar  03
A2 text2  NY   Feb  02
A1 text1  SG   Jan  01
A1 text1  AUS  Jan  01

##</code><code>##

A1 text1  NY:SG:AUS   Jan  01
A2 text2  LN:NY       Feb  02
A3 text3  SG          Mar  03

##</code><code>##

use warnings;
use strict;

my %hash;

while (<DATA>){
    chomp;
    my ($key, $col2, $col3) = split;
    push @{ $hash{$key}{$col2} }, $col3;
}

for my $k (keys %hash){
    for (keys %{ $hash{$k} }){
        my $cols3 = join ':', @{ $hash{$k}{$_} };
        print "$k $_ $cols3\n";
    }
}