Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Greetings Monks,

I need to transpose a bi-dimentional array, so that rows become columns and vice-versa.

my @matrix = (
   [ qw(ab cd ef gh)],
   [ qw(ij kl mn op)],
   [ qw(qr st uv wx)]
);

# should become
my @transposed = (
   [ qw(ab ij qr)],
   [ qw(cd kl st)],
   [ qw(ef mn uv)],
   [ qw(gh op wx)]
);

[download]

I found Math::Matrix, which has a "transpose" method. However, it only works with numerical matrices, and since my matrices are mostly text, I was wondering if there are any general purpose methods (or modules) to achieve this goal.

Thanks

20030721 Edit by Corion: Changed title from 'Transpose a bi-dimentional array'

Replies are listed 'Best First'.
Re: Transpose a bi-dimensional array
by dbwiz (Curate) on Jul 21, 2003 at 11:24 UTC

    tye has written a tool that should serve your purpose. Have a look at mapcar

    use mapcar;

my @matrix = (
   [ qw(ab cd ef gh)],
   [ qw(ij kl mn op)],
   [ qw(qr st uv wx)]
);

my @transposed = mapcar {[@_]} @matrix;

print join( "  ", @$_), $/ for @transposed;

__END__
ab  ij  qr
cd  kl  st
ef  mn  uv
gh  op  wx

    [download]
    Update
    mapcar is now a function in tye's Algorithm::Loops.

    The above example would becpme:

     
use Algorithm::Loops qw(MapCar);

my @matrix = (
   [ qw(ab cd ef gh)],
   [ qw(ij kl mn op)],
   [ qw(qr st uv wx)]
);

my @transposed = MapCar {[@_]} @matrix;

print join( "  ", @$_), $/ for @transposed;

    [download]

    With exactly the same result.

[reply]
[d/l]
[select]
Re: Transpose a bi-dimensional array
by edan (Curate) on Jul 21, 2003 at 11:28 UTC

    Or, you could just peek in the source of Math::Matrix, nick the transpose() method, un-OO-ify it, and ... voila!

    #!perl -l

my @matrix = (
  [ qw(ab cd ef gh)],
  [ qw(ij kl mn op)],
  [ qw(qr st uv wx)]
);

my $transposed = transpose(\@matrix);
local $" = ",";
print "@$_" for @$transposed;


sub transpose {
    my $matrix = shift;
    my @result;
    my $m;

    for my $col (@{$matrix->[0]}) {
        push @result, [];
    }
    for my $row (@{$matrix}) {
        $m=0;
        for my $col (@{$row}) {
            push(@{$result[$m++]}, $col);
        }
    }

    return \@result;
}

    [download]

    Disclaimer: not my coding style! I just modified existing code to make a point (Use the Source, Luke)

    --
    3dan
[reply]
[d/l]
Re: Transpose a bi-dimensional array
by Abigail-II (Bishop) on Jul 21, 2003 at 12:35 UTC
    A totally different way than already presented using tie: 
    package Tie::Transpose;

use strict;
use warnings;

sub TIEHASH  {bless $_ [1] => $_ [0]}
sub FETCH    {my ($y, $x) = split /$;/ => $_ [1]; $_ [0] [$x] [$y]}
sub STORE    {die}


package main;

my $matrix = [[qw /ab cd ef/],
              [qw /gh ij kl/],
              [qw /mn op qr/],
              [qw /st uv wx/]];

tie my %trans => 'Tie::Transpose', $matrix;

print $trans {0, 0}, "\n";
print $trans {0, 1}, "\n";
print $trans {0, 2}, "\n";
print $trans {0, 3}, "\n";
__END__
ab
gh
mn
st

    [download]

    You may want to work out some details before putting this in production code.

    Abigail

[reply]
[d/l]
Re: Transpose a bi-dimensional array
by broquaint (Abbot) on Jul 21, 2003 at 11:31 UTC
    With a liberal use of map then we get the following code 
    use Data::Dumper;

my @matrix = (
  [ qw(ab cd ef gh)],
  [ qw(ij kl mn op)],
  [ qw(qr st uv wx)]
);

my @transposed = map {
  my $i = $_;
  [ map $matrix[$_]->[$i], 0 .. $#matrix ]
} 0 .. $#{$matrix[0]};

print Dumper(\@transposed);

__output__

$VAR1 = [
          [
            'ab',
            'ij',
            'qr'
          ],
          [
            'cd',
            'kl',
            'st'
          ],
          [
            'ef',
            'mn',
            'uv'
          ],
          [
            'gh',
            'op',
            'wx'
          ]
        ];

    [download]
    Not as elegant as dbwiz's solution, but effective nonetheless.
    HTH

    _________
    broquaint

[reply]
[d/l]
Re: Transpose a bi-dimensional array
by jmcnamara (Monsignor) on Jul 21, 2003 at 11:29 UTC

    Here is one way: 
        #!/usr/bin/perl -wl

    use strict;
    use Data::Dumper;

    my @matrix = (
       [ qw(ab cd ef gh)],
       [ qw(ij kl mn op)],
       [ qw(qr st uv wx)]
    );

    my @transpose;
    for my $aref (@matrix) {
        my $i = 0;
        push @{$transpose[$i++]}, $_ for @$aref;
    }

    print Dumper(@matrix);
    print Dumper(@transpose);

    __END__

    [download]

    --
    John.

[reply]
[d/l]
      Hi John, How to print the data to the specific file instead of in terminal? Thanks Anil
[reply]
[reply]

Back to Seekers of Perl Wisdom