Transpose of a Matrix in Perl

The following script performs the transposition of a matrix in Perl. Launched without arguments, the program transpose.pl prints the syntax for execution. In this case, we get the following output:

Usage: transpose.pl [ -p ] datafile
    -p    prints original matrix

The script requires one or two arguments. At least one valid file must be provided. The ‘-p’ option is optional and allows the original matrix to be printed to the terminal.

Create a sample matrix inside a file called ‘matrix’:

a b c d e
f g h i j
k l m n o

Now we can run the script by giving the name of the file we just created as an argument. Remember to give execute permissions to the file:

$ ./transpose.pl matrix
a  f  k
b  g  l
c  h  m
d  i  n
e  j  o

Executed with the ‘-p’ option, we get the following result:

$ ./transpose.pl -p matrix
Original matrix
a  b  c  d  e  
f  g  h  i  j  
k  l  m  n  o  

Transpose matrix
a  f  k  
b  g  l  
c  h  m  
d  i  n  
e  j  o  

Below is the complete code:

#!/usr/bin/perl

# transpose.pl ---
#
# Filename: transpose.pl
# Description: generates de transpose od a matrix
# Author: Francisco Yepes Barrera
# Maintainer: Francisco Yepes Barrera
# Created: Thu Jul 31 08:46:27 2025 (+0200)
# Version: 1.0
# Package-Requires: (strict)
# Last-Updated: Thu Jul 31 12:15:27 2025 (+0200)
#           By: Francisco Yepes Barrera
#     Update #: 40
# URL: https://www.godelia.org
# Keywords: transpose, matrix
#
#

# Commentary:
#
# For comments write an email to <paco.yepes@godelia.org>
#
#

# Change Log:
#
#
#
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or (at
# your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
#
#

# Code:

use strict;

if ( @ARGV < 1 || @ARGV > 2 ) {
	print
	    "Usage: transpose.pl [ -p ] datafile\n";
	print "    -p    prints original matrix\n";
	exit;
}

my ($r, @data, $n, $datafile, $print_original);

if ($ARGV[0] eq '-p') {
	$print_original = 1;
	$datafile = $ARGV[1];
} elsif ($ARGV[1] eq '-p') {
	$print_original = 1;
	$datafile = $ARGV[0];
} else {
	$print_original = 0;
	$datafile = $ARGV[0];
}

if ($print_original) {
	print "Original matrix\n";
}

open(IN, $datafile);

$r = 0;

while (<IN>) {
	next if ( /^\#/ || /^\%/ );
	chop;

	my @a = split(/\s+/);
	$n = 0;

	foreach (@a) {
		$data[$n][$r] = $a[$n];

		if ($print_original) {
			print "$data[$n][$r]  ";
		}

		$n++;
	}

	if ($print_original) {
		print "\n";
	}

	$r++;
}

close(IN);

if ($print_original) {
	print "\nTranspose matrix\n";
}

for (my $i = 0; $i < $n; $i++) {
	for (my $j = 0; $j < $r; $j++) {
		print "$data[$i][$j]  ";
	}

	print "\n";
}

#
# transpose.pl ends here