Thanks all for your suggestions!
I never used 'eval', but from what I've read, it seems like a good thing!
The recursive way of doing it has nothing wrong, but I was wondering if there were other ways - to learn new tricks :)
Thanks again! Maybe I can actually post the recursive way: 

my @array_2D = blablabla
my ($tree, $tmp);

foreach my $row (@array){
    $tmp = extend_MTree($row);
    $tree = add($tmp, $tree);
}

$tree now contains the hash!

sub extend_MTree($)
  {
    my ($a) = @_;

    my %H_tmp;

    if( $#{$a} == -1)
      {
    return 1;
      }

    my $elmt = shift @$a;
    $H_tmp{$elmt} = extend_MTree($a);
    return \%H_tmp;
  }

sub add()
  {

    my ($tmp, $res) = @_;

    foreach my $key (keys %$tmp)
      {

    # this is a new path, add here and leave
    if(!defined($res->{$key}))
      {
        $res->{$key} = $tmp->{$key};
        return $res;
      }

    # this part of the path exists, recurse
    $res->{$key} = add($tmp->{$key}, $res->{$key});
    return $res;
      }

[download]

In reply to Re^2: How to transform a matrix into a hash?? by yocoim
in thread How to transform a matrix into a hash?? by yocoim

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