Limbic~Region has asked for the wisdom of the Perl Monks concerning the following question:

All:
While tracking down an interesting bug in some of my code, I discovered that while chomp can take a list such as an array, it doesn't work quite right on an AoA. Consider the following: 

#!/usr/bin/perl -w
use strict;
my @Fields;
my @Array;
open (FILE,"file") or die "Can't open file\n";
while (<FILE>) {
  next if (/^#/);
  @fields = split "\t" , $_;
  next unless (@Fields == 7);
  push @Array , [ @Fields[0,3,6] ];
}
foreach my $foo (@fields) {
  print "$foo->[2]\n" if ($foo->[2] != 3);
}

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You are confused as to why the code won't work (scratching head) - oh, I see my mistake - there is a trailing newline at the end - let me just get rid of it. 

  push @Array , [ @Fields[0,3,6] ];
}
chomp @Array;
foreach my $foo (@fields) {
  print "$foo->[2]\n" if ($foo->[2] != 3);
}

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Now it still doesn't work - this time you are getting some error about not being able to use a stringified array as a reference with strict enforced.

you remove the chomp as is and you put it back in the code that builds the array 

while (<FILE>) {
  next if (/^#/);
  @fields = split "\t" , $_;
  next unless (@Fields == 7);
  chomp $Fields[6];
  push @Array , [ @Fields[0,3,6] ];
}

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You are happy your code is now working, but you are sad that you have to do it THAT way.

so friendly monks - is there a way to chomp an AoA similar to: 

chomp @Array;

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Thanks in advance - L~R

Replies are listed 'Best First'.
Re: Chomp an AoA?
by Gilimanjaro (Hermit) on Jan 28, 2003 at 20:49 UTC
    First of all, why would you want to chomp anything that did not directly result from a <> read? perlfunc states that chomp chomps a trailing $/, which you are guaranteed only to see when reading using <> brackets... I always do the chomp as the first statement in the loop. When I'm in a daring mood I even put it in the while clause...

    Secondly, I think you might be mistaking an array for a list... Which I always did until I read Arrays are not lists by tilly. If that is the case, then chomp would probably work if you did:

    chomp @Array[0..$#Array];

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    If that ain't it, I humbly apologize... :)

    Update: Read original post again; seems logical to me chomp won't work as you suggest; an AoA is really an AoRA (Array of references to arrays) and you can hardly expect chomp to merily go dereferencing elements of the array it's passed...

    I am now even more so convinced the chomp should just be moved up in the loop, where it belongs...

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      You are exactly right. He should be chomp'ing in his while loop, right between next unless (@Fields == 7); and push @Array , [ @Fields[0,3,6] ];. A nice juicy chomp @Array;

      MJD says you can't just make shit up and expect the computer to know what you mean, retardo!
      ** The Third rule of perl club is a statement of fact: pod is sexy.

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Re: Chomp an AoA?
by chromatic (Archbishop) on Jan 28, 2003 at 21:53 UTC

    chomp works on a list of strings. An array of array references listifies to a list of array references, which are stringified, which doesn't do what you want.

    Why not just chomp each line as you read it, before you split it?

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Re: Chomp an AoA?
by integral (Hermit) on Jan 28, 2003 at 19:16 UTC
    A simple way of coding this inline would be to do a 
    map { chomp @$_ } @_;

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    But while this would solve your problem isn't not a generic recursive chomp.

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Re: Chomp an AoA?
by dempa (Friar) on Jan 28, 2003 at 19:10 UTC

    Maybe not the answer you want, but I would use Juerds snippet for this.

    Semi-OT random ramblings: I took Juerds snippet and modified it into two new functions: base64_encode_struct and base64_decode_struct. Instead of chomp:ing the data I encoded/decoded it with MIME::Base64. Useful if you have a complex data structure that you want to use with XML::Simple but you want to Base64-encode the data (not the tags).

    -- 
    dempa

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Re: Chomp an AoA?
by Aristotle (Chancellor) on Jan 31, 2003 at 03:18 UTC
    To chomp all elements you could 
    chomp @$_ for @array;
# or
chomp map @$_, @array;

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    However since you only want to chomp one of them 
    chomp map $_->[2], @array;

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    But why add another loop if you can do it inline? 
    while (<FILE>) {
    next if /^#/ or tr/\t// != 6;
    chomp;
    push @array, [ split "\t" ];
}

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    Makeshifts last the longest.

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