Perl: Sort Matrix

By Xah Lee. Date: . Last updated: .

Here's a function that can sort a matrix in all possible ways.

This Perl version i wrote in 1999, and was used in production of a ecommerce server.

# -*- coding: utf-8 -*-
# perl

=pod

sort_matrix( $matrix, [[$n1, $stringQ, $directionQ], [$n2, $stringQ,
$directionQ], …]) sorts a matrix by $n1 th column then $n2 th…and
so on.

$matrix must be a reference to references of arrays, having the form
[[$e1, $e2,…], […], …].  $stringQ is a boolean indicating
whether to treat corresponding columns as a strings instead of as
number in the sorting process. True means string. $directionQ is a
boolean indicating ascending sort or not for the corresponding
column. In the column spec $n1 $n2 …, index counting starts at 0.

 Example:

 my $ref_matrix =
 [
   [3, 99, 'a'],
   [2, 77, 'a'],
   [1, 77, 'a']
 ];

sort_matrix( $ref_matrix,  [ [2,1,1], [1,0,1] ]);
# this means sort by third column, regarding it as strings, 
# and in ascending order. If tie, sort by second column, 
# regarding it as number, in ascending order.

# returns [[2,77,'a'],[1,77,'a'],[3,99,'a']];

=cut


sub sort_matrix($$) {
    my $ref_matrix = $_[0];
    my @indexMatrix = @{$_[1]};

    my @indexes = map {$_->[0]} @indexMatrix;
    my @operators = map {$_->[1] ? ' cmp ' : ' <=> '} @indexMatrix;
    my @directions = map {$_->[2]} @indexMatrix;

    my $body_code = '';
    my @body_array;
    for (my $i = 0; $i <= $#indexes; $i++) {
        if ($directions[$i]) {
            push(@body_array, "(\$a->[$i]" . $operators[$i]  . "\$b->[$i])");
        } else {
            push(@body_array, "(\$b->[$i]" . $operators[$i]  . "\$a->[$i])");
        };
    };
    $body_code = join( ' or ', @body_array);

    my $array_code = '(map { [' . join(q(, ), map {"\$_->[$_]"} @indexes) . ', $_]} @$ref_matrix)';

    my $code = "map {\$_->[-1]} (sort { $body_code} $array_code)";
    my @result = eval $code;
    return [@result];
};

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