dr_jgbn,
When I see the words ultra efficient script - I think that this is either:
  • A case not to use Perl
  • Perl is fine and you are paranoid about premature optimization

    With that said and given your example data - I would: 

    #!/usr/bin/perl -w
use strict;
my %seen;
my @data;
open (INPUT,"file") or die "Error accessing file : $!";
while (<INPUT>) {
    chomp;
    my ($col1, $col2) = split /\t/;
    if (exists $seen{$col1}) {
        $data[$seen{$col1} - 1] .= " $col2";
    }
    else {
        $seen{$col1} = push @data , "$col1\t$col2";
    }
}
print "$_\n" foreach(@data);

    [download]

    Cheers - L~R

    Update: Completely re-wrote code to be unique as my original solution closely mirrored others

  • Use array instead of hash to store data
  • Use hash to determine array element
  • Use fact that push returns new number of elements to store in hash

    In reply to Re: Removing redundancy by Limbic~Region
    in thread Removing redundancy by dr_jgbn

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