=pod

B<sort_matrix>

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

$matrix must be a reference to references of arrays, having the form 
[[$n1, $n2,...], [...], ...].  $stringQ is a boolean indicating the 
corresponding column is a string or not. $directionQ is a boolean 
indicating ascending sort or not for the correpsonding column. 
Important: Index counting starts at 0.

 Example:

 my $ref_matrix =
 [
   [3, 99, 'b'],
   [2, 77, 'c'],
   [1, 66, 'a']
 ];

 # sort by third column, then second column.
sort_matrix( $ref_matrix,  [ [2,1,1], [1,0,1] ]);

 # returns   [[1,66,'a'],[3,99,'b'],[2,77,'c']];

=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];
};