for loop trouble

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

Hi Monks,

I can't work out what is wrong with my loop. I'm simply iterating through an array called @pids (630 items). I want to get those items that match things in a different array and those that don't seperately.

I get 400 items in @hits as expected but the full 630 items in the @potential_hgt array (when it should be finding 230).

Can someone please advise where i'm going wrong?

cheers

foreach my $orth (@orthologs)   {
        my $hit;
        if ($orth =~ /^A(\d+)/) {
        $hit=$1;
        }
                                                                      
+                                                                     
+                           
        for (my $i=0; $i<@pids; $i++)   {
                if ($pids[$i] =~ /$hit/)        {
                        push @hits, $hit;
                }
                else    {
                        push @potential_hgt, $pids[$i];
                }
        }
}
[download]

Comment on for loop trouble Download Code

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Re: for loop trouble by Corion (Patriarch) on Aug 12, 2005 at 09:59 UTC
Your `$hit` variable is undefined if your `$orth` variable doesn't match `/^A(\d+)/`. You might want to check for that. Also, you seem to come from a C-like programming language. The loop could be written in a shorter, less error-prone way as `push @hits, grep {/$hit/} @pids; push @potential_hgt, grep {! /$hit/} @pids;` [download] There also is a module which implements the `part` function, which divides one list into two (or more) lists, which would be quite handy here, but I don't find that module at the moment.	[reply] [d/l]
Re^2: for loop trouble by fishbot_v2 (Chaplain) on Aug 12, 2005 at 13:00 UTC
There also is a module which implements the part function... see: List::Part `use List::Part; my ( $in, $out ) = part { m/$hit/ } @pids;` [download] Where `$in` is an arrayref to the matches, and `$out` to the rest.	[reply] [d/l] [select]
Re^2: for loop trouble by Roy Johnson (Monsignor) on Aug 12, 2005 at 15:03 UTC
It's not at all onerous to implement part doing just one pass, without a module: `push @{/$hit/ ? \@hits : \@potential_hgt}, $_ for @pids;` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re: for loop trouble by ambrus (Abbot) on Aug 12, 2005 at 10:01 UTC
I guess your problem may be that you put all pids in `@potential_hgt` whenever it doesn't match an `$orth`. Is it possible that you wanted to put there only those that don't match any of the `@orthologs`?	[reply] [d/l] [select]
Re: for loop trouble by graff (Chancellor) on Aug 12, 2005 at 15:23 UTC
If I understand the task correctly, I think you'll be better off nesting the loops this way (not tested): `# build the list of targets my @targets = map { /^A(\d+)/; $1 } @orthologs; # go through @pids and segregate them into @hits and @potentials my @hits = my @potentials = (); for my $p ( @pids ) { my $itsahit = 0 for my $t ( @targets ) { if ( $p =~ /$t/ ) { push @hits, $t; $itsahit++; last; } } push @potentials, $p unless ( $itsahit ); }` [download]	[reply] [d/l]