multi-dimensional arrays, dereferencing

[fabalicious]

the following code compares the sequences $s and $t and calculates a 2-dim matrix containing the lengths of matching substrings at the position of the last matching characters. I don't know how to dereference in the nested foreach loop at the bottom in order to go through the matrix scalar by scalar.

$s = "evian-eauminerale";
$t = "borisvian-ecrivain";

foreach my $i (1..length($s)) {
         foreach my $j (1..length($t)) {
                if (substr($s, $i-1, 1) eq substr($t, $j-1, 1)) {
                   $M[$i][$j] = $M[$i-1][$j-1]+1;
                   $M[$i-1][$j-1] = 0;
                }
        }
}

foreach @array (@M) {
        foreach $element (@array) {
                print "$element ";
        }
        print "\n";
}

[thinker]

Hi fabalicious

If @M is an array of array references, then

foreach $arrayref (@M) {
        foreach $element (@$arrayref) {
                print "$element ";
        }
        print "\n";
}

hope this helps

cheers

thinker

[Skeeve]

#untested!
foreach $aref (@M) {
        foreach $element (@$aref) {
                print "$element ";
        }
        print "\n";
}

[thinker]

Hi fabalicious

As an aside, and this is merely a matter of style, your method of doing what you want to do is very verbose.

I would choose to write it as

print "@$_\n" for @M;

taking advantages of some of some not so intuitive Perl idioms, like using @$_ to dereference each array, and the fact that "@array" will join the elements of @array with $", which is a space by default. And it saves you printing an extra space character at the end of each line :-)

In the spirit of TMTOWTDI

cheers

thinker

[fabalicious]

Cheers to skeeve and thinker. Still doesn't look very obvious to me, but it does the job.

[thinker]

Hi fabalicious

For a good explaination, see

perldoc perllol
perldoc perlreftut

hope this helps

cheers

thinker

[Not_a_Number]

I would add

perldoc perldsc

And it happens that the free online chapter from merlyn's new book Learning Perl Objects, References and Modules covers this very topic. Check it out on the O'Reilly website.

NB: that shouldn't stop you from buying the book :-)

dave

[Skeeve]

An "array of arrays" is in fact an array of references to arrays. So each element of your @M is an array reference leading us to:

foreach $aref (@M) {...

To get the actual array from an array reference, one usually writes @$aref leading us to

    foreach $element (@$aref) {...

and that's all about it.