perl compare elements of arrays and grouping

arrays, compare, perl

Solution

You appear to have overcomplicated this a bit more than it needs to be, but that's common for beginners. Think more about how you would do this manually:

- Look at each line.

- See whether the third and fifth fields are the same as the previous line.

- If so, print them.

The looping and all that is completely unnecessary:

#!/usr/bin/env perl

use strict;
use warnings;

my ($previous_row, $third, $fifth) = ('') x 3;

while (<DATA>) {
  my @fields = split;
  if ($fields[2] eq $third && $fields[4] eq $fifth) {
    print $previous_row if $previous_row;
    print "\t$_";
    $previous_row = '';
  } else {
    $previous_row = $fields[0] . "\t" . $_;
    $third = $fields[2];
    $fifth = $fields[4];
  }
}

__DATA__
1 L DIELTQSPE H EVQLQESDAELVKPGASVKISCKASGYTFTDHE
2 L DIVLTQSPRVT H EVQLQQSGAELVKPGASIKDTY
3 A ALQLTQSPSSLSAS B RITLKESGPPLVKPTCS C ELDKWAN
4 A ALQLTQSPSSLSAS B RITLKESGPPLVKPTCS C ELDKWAG
5 A ALQLTQSPSSLSAS B RITLKESGPPLVKPTCS C LELDKWASL
6 L DIQMTQIPSSLSASLSIC H EVQLQQSGVEVKMSCKASGYTFTS
7 L SYELTQPPSVSVSPGSIT H QVQLVQSAKGSGYSFS P YNKRKAFYTTKNIIG
8 L SYELTQPPSVSVSPGRIT H EVQLVQSGAASGYSFS P NNTRKAFYATGDIIG
9 A MPIMGSSVAVLAIL B DIVMTQSPTVTI C EVQLQQSGRGP
10 A MPIMGSSVAVLAIL B DIVMTQSPTVTI C EVQLQQSGRGP
11 L DVVMTQTPLQ H EVKLDESVTVTSSTWPSQSITCNVAHPASSTKVDKKIE
12 A DIVMTQSPDAQYYSTPYSFGQGTKLEIKR

(Note that I changed line 10 slightly so that its third field will match line 9 in order to get the same groups in the output as specified.)

Edit: One line of code was duplicated by a copy/paste error.

Edit 2: In response to comments, here's a second version which doesn't assume that the lines which should be grouped are contiguous:

#!/usr/bin/env perl

use strict;
use warnings;

my @lines;
while (<DATA>) {
  push @lines, [ $_, split ];
}

# Sort @lines based on third and fifth fields (alphabetically), then on
# first field/line number (numerically) when third and fifth fields match
@lines = sort { 
  $a->[3] cmp $b->[3] || $a->[5] cmp $b->[5] || $a->[1] <=> $b->[1] 
} @lines;

my ($previous_row, $third, $fifth) = ('') x 3;
for (@lines) {
  if ($_->[3] eq $third && $_->[5] eq $fifth) {
    print $previous_row if $previous_row;
    print "\t$_->[0]";
    $previous_row = '';
  } else {
    $previous_row = $_->[1] . "\t" . $_->[0];
    $third = $_->[3];
    $fifth = $_->[5];
  }
}

__DATA__
1 L DIELTQSPE H EVQLQESDAELVKPGASVKISCKASGYTFTDHE
3 A ALQLTQSPSSLSAS B RITLKESGPPLVKPTCS C ELDKWAN
2 L DIVLTQSPRVT H EVQLQQSGAELVKPGASIKDTY
5 A ALQLTQSPSSLSAS B RITLKESGPPLVKPTCS C LELDKWASL
7 L SYELTQPPSVSVSPGSIT H QVQLVQSAKGSGYSFS P YNKRKAFYTTKNIIG
6 L DIQMTQIPSSLSASLSIC H EVQLQQSGVEVKMSCKASGYTFTS
9 A MPIMGSSVAVLAIL B DIVMTQSPTVTI C EVQLQQSGRGP
8 L SYELTQPPSVSVSPGRIT H EVQLVQSGAASGYSFS P NNTRKAFYATGDIIG
11 L DVVMTQTPLQ H EVKLDESVTVTSSTWPSQSITCNVAHPASSTKVDKKIE
10 A MPIMGSSVAVLAIL B DIVMTQSPTVTI C EVQLQQSGRGP
12 A DIVMTQSPDAQYYSTPYSFGQGTKLEIKR
4 A ALQLTQSPSSLSAS B RITLKESGPPLVKPTCS C ELDKWAG

Problem

Original source