Given the data is ordered as you show, this should do what you want: 

my %data;

while (<DATA>) {
    chomp($_);
    my ($first, $second) = split(/\s+/, $_);
    push(@{$data{$first}}, $second);
}

foreach my $first (sort {$a <=> $b} keys %data) {
    print "$first ", join('-', @{$data{$first}}), "\n";
}

[download]

Hope this helps, -gjb-

In reply to Re: Group 2d array by gjb
in thread Group 2d array by Anonymous Monk

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