I have a file for which I need to remove some rows for which there is an element of duplication.
Example file (tiny compared to the real thing). 
d1 c1.1  f1  d1.1
d1 c1.1  f2  d1.2
d2 c1.1  f1  d1.1
d3 c1.1  f1  d1.1
d4 c1.1  f1  d1.1
d4 c1.1  f2  d1.2
d5 c1.1  f4  d1.4
d6 c1.1  f5  d1.5

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For each c1.1 group, I want a print out whereby for each c1.? all duplicate d1.? entries are removed. In other words I'm after something like this 
d1 c1.1  f1  d1.1
d1 c1.1  f2  d1.2
d5 c1.1  f4  d1.4
d6 c1.1  f5  d1.5

[download]
The print out should include all four columns Here is what I've attempted so far 
#!/usr/bin/perl -w

use strict;
use warnings;
use English;
use FileHandle;

use Exception;

my ($fIn) = $ARGV[0];
    
open(FILE, "$fIn") || die "ERROR: Can't open $fIn  file: $!\n";
    
my %hash;

my $c_id;
my $d_id;
my $f_var;

while(<FILE>)
{
   chomp;

   my @data = split(/\s+/, $_);

   $c_id = $data[1];
   $d_id = $data[3];
   $f_var = $data[2];

   if(!$hash{$c_id}{$f_var})
   {
     $hash{$c_id}{$f_var} = $d_id;

    }

 }

while (( my $k1, my $k2) = each %hash)
{
    print "$k1 ";
    while (( $k2, my $k3) = each %$k2)
    {

    print "$k2 $k3 ";
    }
    print "\n";

}

[download]
But sadly I'm getting an error about not being able to use a string as a HASH ref while 'strict refs' are in use. Could someone please point me in the right direction? Thanks

In reply to Trying to remove duplicate rows using hashes by Angharad

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