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

Dear Monks, I am new to hashes etc and wondered if you could help. I have two arrays placed in a hash: one contains numbers, the other contains + and - signs related to each number. I have a third array not in the hash which i am using to compare to the numbers in the hash and extract the corresponding sign when they match. I know that hashes are mixed up (e.g. not in insertion order), but when my number matches, not only would I like to extract the corresponding sign, but i would also like to extract the next sign in the sequence e.g $i and $i+1 - this is the part that i'm confused about. Here's my code below - hope you can help ! 

my %hash = map { $numbers[$_] => $signs[$_]} 0 .. $#numbers;

while (($key, $value) = each (%hash))  {

      if (@new_numbers)   {
              for (my $i=0; $i<@new_numbers; $i++)   {
                     if ($key == $new_numbers[$i])   {
                             print "$value \t $new_numbers[$i]";  # th
+is prints the sign and the number it matches to
                     }
              }
      }

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Re: hash problems
by murugu (Curate) on Jul 08, 2004 at 11:09 UTC

    May be I have misunderstood the question,

    I have made some variations in ur code. Instead of using hashes i have used arrays. 

    @numbers=(1,2,3,4);
@signs=('+','-','*','+');
@thirdarray=(2,3);

my @new = map { [$numbers[$_],$signs[$_]]} 0 .. $#numbers;


foreach my $i (0..$#new)
{
print $new[$i+1]->[0],$new[$i+1]->[1]."\n" if (grep{/^$new[$i]->[0]$/}
+@thirdarray);
}

    [download]

    Cheers.

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[d/l]
      thanks murugu, i think i want something like this but i have tried it and it doesn't quite do it. from your example, the desired output would be: 
      2-+
3++

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      How could i modify your code to do this? Many many thanks
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Re: hash problems
by PerlingTheUK (Hermit) on Jul 08, 2004 at 11:13 UTC
    If I understand yout Problem right this might do: 
    my $ptr;
for ( my $i = 0; $i < @numbers; $i++ ){

 $ptr->{$i}->{ number } = $numbers[$i];
 $ptr->{$i}->{ sign }   = $signs[$i];

}

    [download]
    This is a reference for a hash. You can now get your values back as: 
    while (@new_numbers){
 my $i = $_;
 if ( defined $ptr->{$i} ){
  print $ptr->{$i}->{ sign }.$ptr->{$i}->{ number }."\t".$i;
 }
}

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    This is not tested but should work. It uses references to a hash. Alternatively you might want to make $i part of the keys: 
    $hash{ $numbers[$i].":".$i } = $signs[$i];

    [download]
    But it would be much more complicated sorting the keys out. Hope this is what you wanted.
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Re: hash problems
by Roy Johnson (Monsignor) on Jul 08, 2004 at 14:04 UTC
    Do you just want to 
    print "$value \t $new_numbers[$i] $new_numbers[$i+1]\n";

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    ? You would want to modify your for loop range (as you should, anyway) so that $i+1 doesn't go beyond the actual array. Instead of $new_numbers[$i+1], you might want $hash{$key+1}. It's hard to tell what you expect your code to do. What is @new_numbers?
    We're not really tightening our belts, it just feels that way because we're getting fatter.
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Re: hash problems
by perldeveloper (Scribe) on Jul 08, 2004 at 11:11 UTC
    If the order matters, then you'll have to use arrays. Better assign two keys to your $hash, one for an array of numbers (say @{$hash->{numbers}}) and one for an array of signs (@{$hash->{signs}}). Then look within the numbers array (@{$hash->{numbers}}, find the corresponding $i (that is $hash->{numbers}->[$i]) and extract the two signs: $hash->{signs}->[$i] and $hash->{signs}->[$i + 1].
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