I have been using some of this syntax. I was trying to also output a unique count of the numbers in the 3rd & 4th columns. I was trying to push the value's in the column onto an array, if it already is not already in the array. I think this is currently a scalar value but i would need an array/list. This is the error that I receive: Not an ARRAY reference at ./test.pl line 21, <DATA> line 1. I am thinking once I have the values in an array or list I can just print the list in scalar context to get the unique count? I don't know if there is a simpler way to achieve this.

#!/usr/bin/perl

use strict;
use warnings;

my $basecol=shift @ARGV or die "What base col?";
my %h;
$basecol--; # zero based inside program.
while (<DATA>){
  chomp;
  my @f= split ;
  next unless @f > 1;
  splice @f,0,0,$f[0] . "_". $f[1];
  my $k = $f[$basecol];
  $h{$k}{COUNT}++;
  for my $col(0..$#f){
    next if $col==$basecol;
    $f[$col]=0  unless $f[$col]=~/^\d+$/;
    $h{$k}{FIELD_S}[$col]+= $f[$col];
    push($h{$k}{FIELD_C}[$col],$f[$col]) if !($f[$col] ~~ $h{$k}{FIELD
+_C}[$col]);
  }
}

for (sort keys %h){
  print "$_\t $h{$_}{COUNT}\t";
  for my $f(@{ $h{$_}{FIELD_S} }){
     defined $f or $f='';
     print "$f\t";
  }


  print "\n";
}
__DATA__
U1     ID1     100     280
U1     ID1     137     250
U2     ID2     150     375
U1     ID2     100     100
U3     ID1     100     600
U9     ID3     137     200
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