confusing number of elements in an array

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

Hi!

I can't understand why the following code outputs as if the array had only one element.

Does it really have just one element? If yes, why? (since I call the sorter sub 2 times)

If I take out the my's it outputs as having 3 elements. Really confused. Here is the code:

#!/usr/bin/perl

use strict;


my $lineA = "CTACACTTCCATGACCACACATTAATAATTGTGTTCCTAATTAGCTCATTAGTACTC
+TAC";
my $lineB = "CTACACTTTCACGATCATACACTAATAATCGTTTTTCTAATTAGCTCTTTAGTTCTC
+TAC";

sub altrIter{return (($_[0] % 10)) };
sub altrInc {return ($_[0]+1) };

&sorter ($lineA, \&altrIter, \&altrInc);
&sorter ($lineB, \&altrIter, \&altrInc);

my @allSeq;
my $index=0;

sub sorter {
    my $i = &{$_[1]}($index);
    $allSeq[$i]= ($allSeq[$i].$_[0]);
    $index =  &{$_[2]}($index);
    print "in: ".$_[0]."\n";
}

for (my $i = 0; $i <= $index; $i++){
    print "seq -->".$allSeq[$i]."\n";
}
[download]

Thanks for any help.

Comment on confusing number of elements in an array Download Code

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Re: confusing number of elements in an array by chromatic (Archbishop) on Apr 05, 2007 at 17:17 UTC
`$index` gets reset to zero before the final loop. Notice that your calls to `sorter()` occur in the code before the assignment to `$index`. Moving your code around will help. A better idea is to use native iteration, though, as you don't use the array index: `for my $seq (@$allSeq) { print "seq -->$seq\n"; }` [download] (As a style note, I spent a lot of time deciphering your code; using variable names in your subroutines for parameters would really help. Also, I find it much easier to call subs by reference with the `$subref->( @args )` syntax; it's much less visually cluttered.) Update: ikegami pointed out a typo.	[reply] [d/l] [select]
Re: confusing number of elements in an array by ambrus (Abbot) on Apr 05, 2007 at 17:14 UTC
I think there are two problems with your code. The more serious one is that you initialize the $index variable to zero after you increment it by calling sorter. Thus, $index will be zero by the time you print the array. The lesser problem is an off-by-one error in the for loop: the halting condition should be `$i < $index`, as $index points after the last element of the array.	[reply] [d/l]
Re: confusing number of elements in an array by kyle (Abbot) on Apr 05, 2007 at 17:21 UTC
Your output loop uses `$index`, and you set `$index=0` after your calls to `sorter`. If you want the actual contents of your array without `$index`, you can do that this way: `foreach my $seq ( @allSeq ) { print "seq -->$seq\n"; }` [download] I suggest also that you `use warnings` and that you name the parameters to your subs: `sub sorter { my ( $line, $iter_sub, $inc_sub ) = @_; my $i = $iter_sub->($index); $allSeq[$i] .= $line; $index = $inc_sub->($index); print "in: $line\n"; }` [download]	[reply] [d/l] [select]