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

Hello fellow monks,

I've written the following code snippet to try and demonstrate my problem: 

#!/perl/bin/perl.exe -w
use strict;

use vars qw(@array @data @compare $num );

$num = 0;
for (0 .. 3) {
    @array = ();
    for (0 .. 1) {
        push @array, $num;
    $num ++;
    }
    push @data, [@array];
}
  
@compare = (2, 4, 5, 6);

print "Contents of \@array\n";
foreach my $record (@data) {
  for my $i (0 .. 1) {
    print $record->[$i] . " ";
    }
    print "\n";
}

print "\n\nContents of \@compare\n";
foreach (@compare) {
    print $_, " ";
    }

[download]
I need to compare the two arrays (one being an array of arrays), against another array, more specifically look at the second element of @array against the contents of @compare and eliminate the duplicates from @array.

I should end up with the following values for @array ... 

Contents of @array
0 1
2 3
6 7


Contents of @compare
2 4 5 6

[download]
Notice that the number 5 was the second element in @array Any ideas ?

Replies are listed 'Best First'.
Re: Array element removal
by sauoq (Abbot) on Dec 17, 2002 at 23:27 UTC 
    #!/usr/bin/perl -w
use strict;

# Why go through all that trouble just to init a couple example arrays
+?
my @data    = ( [0, 1], [2, 3], [4, 5], [6, 7], );
my @compare = (2, 4, 5, 6);

# This is the part you want to pay attention to...
my %remove;
@remove{@compare} = ();
my @new = grep { !exists $remove{$_->[1]}  } @data;

# Dump the new array for inspection.
$" = ', ';
print "Contents of \@new    : ( ";
print "[@$_], " for (@new);
print ")\n";

    [download]
    -sauoq
"My two cents aren't worth a dime.";
[reply]
[d/l]
Re: Array element removal
by BrowserUk (Patriarch) on Dec 17, 2002 at 23:31 UTC

    Something like this? 

    #! perl -slw
use strict;
use Data::Dumper;

my @array = ( [0,1],[2,3],[4,5],[6,7]);
my @compare = (2,4,5,6);

@array = map{ $array[$_] if $array[$_][1] != $compare[$_] } 0..$#array
+;

print Dumper \@array;

    [download]

    Examine what is said, not who speaks.

[reply]
[d/l]
Re: Array element removal
by jdporter (Paladin) on Dec 17, 2002 at 23:07 UTC
    It's not clear how you're deciding what arrays should be removed.
    You deleted the third array from @data, because it contained the third element in @compare. That is,    [ 4, 5 ] contains 5  therefore delete. But what if it had been    [ 5, 0 ] Would it get deleted in that case?

    jdporter
    ...porque es dificil estar guapo y blanco.

[reply]
[d/l]
[select]
      Assuming that the critical value has to be in the second position in the array, and if you don't mind building up a new array to replace the old one: 
        my @new_data;
  for my $i ( 0 .. $#data ) {
    $data[$i][1] != $compare[$i] and push @new_data;
  }

  # replace:
  @data = @new_data;

      [download]
      As an aside, you are using global variables unnecessarily. Your code will be a lot clearer and cleaner, and less error prone, if you use lexical variables properly. use warnings; and use strict; to let perl help you write better code.

      jdporter
      ...porque es dificil estar guapo y blanco.

[reply]
[d/l]
[select]

        I assume that he doesn't want the second elements in the arrays referenced in @data to be contained anywhere in @compare. Your code only checks elements in @data and @compare with the same index. The question wasn't very well stated though.

        -sauoq
"My two cents aren't worth a dime.";
[reply]
[d/l]
[select]
      NO, I'm only looking at @array->1 elements
[reply]

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