in reply to Use grep with two arrays

my @keepers;
foreach my $i (0..$#array1)
{
    push @keepers, $i if $array1[$i] =~ /keep these/;
}
@array1 = @array1[@keepers];
@array2 = @array2[@keepers];

[download]

-QM
--
Quantum Mechanics: The dreams stuff is made of

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Re^2: Use grep with two arrays
by revdiablo (Prior) on Feb 14, 2006 at 03:44 UTC

    Just for giggles, here's that using grep:

    my @keepers = grep { $array1[$_] =~ /keep these/ }
              0 .. $#array1;
@array1 = @array1[@keepers];
@array2 = @array2[@keepers];

    [download]
[reply]
[d/l]
      And to avoid the temp variable — not really a valid goal, but kind of fun — and not repeat the grep: 
      my @a1 = qw'only keep ones that have es';
my @a2 = qw'art  bart cart dart eart good';

@a1 = @a1[sort {$a <=> $b} grep {$a1[$_] =~ /e/ or do { splice @a2, $_
+, 1; 0 } } reverse 0..$#a1];
print "@a1\n@a2\n";

      [download]
      It gets a little complicated, mostly because of the gyrations necessary to splice out the right element after others have been removed.
      Caution: Contents may have been coded under pressure.
[reply]
[d/l]
      So to be inefficient and avoid the temp variable (untested): 
      @array1 = @array1[+grep 
                   { $array1[$_] =~ /keep these/ }
                   0 .. $#array1
                 ];
@array2 = @array2[+grep 
                   { $array1[$_] =~ /keep these/ }
                   0 .. $#array1
                 ];

      [download]

      -QM
      --
      Quantum Mechanics: The dreams stuff is made of

[reply]
[d/l]
        Um, I think this suggestion, as you originally posted it, will not work as you intend/expect: 
        @array1 = @array1[+grep 
                   { $array1[$_] =~ /keep these/ }
                   0 .. $#array1
                 ]; 
@array2 = @array2[+grep
                   { $array1[$_] =~ /keep these/ }
                   0 .. $#array1
                 ];

        [download]
        When you process @array2, @array1 is presumably shorter than it used to be -- the elements of the two arrays are no longer in parallel (assuming they were parallel before the first grep operation). You'll be getting the wrong elements left behind in @array2 (only the last elements of @array2 will ever be removed).
[reply]
[d/l]

        And to then avoid reproducing code (which probably negates the advantages of not using a temp variable) (untested):

        @array1 = @array1[slicer(@array1)];
@array2 = @array2[slicer(@array1)];

sub slicer {
    grep 
       { $_[$_] =~ /keep these/ }
       0 .. $#_;
}

        [download]

            -Bryan

[reply]
[d/l]

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