hash problems

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
                     }
              }
      }
[download]

Comment on hash problems Download Code

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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.	[reply] [d/l]
Re^2: hash problems by Anonymous Monk on Jul 08, 2004 at 11:17 UTC
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++` [download] How could i modify your code to do this? Many many thanks	[reply] [d/l]
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; } }` [download] 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.	[reply] [d/l] [select]
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";` [download] ? 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{$key+1}`. It's hard to tell what you expect your code to do. What is @new_numbers? We're not really tightening our belts, it just feels that way because we're getting fatter.	[reply] [d/l] [select]
Re: hash problems by perldeveloper (Scribe) on Jul 08, 2004 at 11:11 UTC
If the order matters, then you'll have to use arrays. Better assign two keys to your `$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]`.	[reply] [d/l] [select]


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