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

Hi Monks.i have a error that i dont understand what is it? please help me.

#!/usr/bin/perl -w
use strict;
my @AoA;     

open (IN,'<result');
while(<IN>){
my @chunks = split;
    push @AoA, [ @chunks[1..$#chunks]];
}

my %neighbours;
for my $domain (@AoA) {
    for my $idx (0 .. $#$domain) {
        my @near = grep {$_ >= 0 && $_ <= $#$domain} $idx - 1, $idx + 
+1;
        push @{$neighbours{$domain->[$idx]}}, map {$domain->[$_]} @nea
+r;
    }
}


open (DOMAINLIST,'<domainlist') or die "cannot open 'domainlist'becuas
+e:$!";

   chomp(my @domain=<DOMAINLIST>);
    for my $domain(@domain){
    my @array=@{$neighbours{$domain}};
    
    @array=removeduplicates(@array);
    my $number=scalar @array;
     print "Domain $domain.......$number\n";
}

sub removeduplicates{
my @array=@_;
my %seen;
$seen{$_}++ for @array;
my @unique = keys %seen;
return @unique;
}

[download]
the error is :cant use an undefined value as an ARRAY reference in line 24.

Replies are listed 'Best First'.
Re: array references
by kennethk (Abbot) on Jul 29, 2011 at 18:48 UTC
    Well, line 24 is:

    my @array=@{$neighbours{$domain}};

    As @{...} is an array dereference, it would appear that $neighbours{$domain} is undefined. I can't tell more without seeing your input (and desired output), but you could at least bandage this with something like: 

        for my $domain(@domain){
    next unless exists $neighbours{$domain};
    my @array=@{$neighbours{$domain}};

    [download]

    Of course, this explicitly skips any element of @domain where %neighbours is uninitialized, which may be problematic for your case. You might also consider something like: 

        for my $domain(@domain){
    my @array=exists $neighbours{$domain} ? @{$neighbours{$domain}} : 
+();

    [download]

    where this second option silently swallows domain misses. See perlreftut for more on references.

[reply]
[d/l]
[select]

      thank you for your help, but it seams the first element in @domain doesnt come to process.

[reply]
        I do not understand what you mean - see How do I post a question effectively?. Specifically, if your code is not behaving as expected, you should post sample input and expected output (both wrapped in <code> tags) so that we can replicate your issue.

        A good bug report is worth a thousand words.

[reply]
[d/l]

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