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Logical operations on arrays

by ronmrdechai (Novice)
on Oct 04, 2012 at 12:16 UTC ( #997226=perlquestion: print w/ replies, xml ) Need Help??
ronmrdechai has asked for the wisdom of the Perl Monks concerning the following question:

Can logical operations be preformed on arrays in perl? (through built in functionality or through a module of some kind)

e.g. (a, b, c) AND (b, c, d) = (b, c).

Google has failed me on this one.

Comment on Logical operations on arrays
Re: Logical operations on arrays
by MidLifeXis (Prior) on Oct 04, 2012 at 12:21 UTC

    If the order of the arrays makes no difference, it sounds like you are looking for an intersection operator of some sort. Array::Utils might have what you are looking for. I found this by searching metacpan for "union intersect".

    Otherwise, a method to find them is pretty straightforward:

    • configure a hash for the first array (*)
      @hash1{@array1} = (1)x@array1
      This configures a hash %hash1 to have a true value for all values found in @array1. (* - This is probably clearer as $hash1{$_} = 1 for @array1)
    • loop through the second array picking out those elements that show up in the first array
      push( @intersection, grep { $hash1{$_} } @array2 );
    There are a couple of assumptions built into the above (@arrayN does not contain an undef value, and the second array only has unique values).

    Updates:

    1. Added example code
    2. Added search example
    3. D'oh - quite right Jenda. I have got to stop writing code before my first cup of coffee. :-/

    --MidLifeXis

      There's no reason to work hard to set the values in the hash to ones, leave them undefined and use exists() within the grep{}. Also there is no reason to push the elements into the @intersection, just assign them.

      my %hash1; @hash1{@array1} = (); my @intersection = grep {exists $hash1{$_} } @array2;

      Jenda
      Enoch was right!
      Enjoy the last years of Rome.

Re: Logical operations on arrays
by daxim (Chaplain) on Oct 04, 2012 at 13:07 UTC
    These are set operations, see Set::Scalar or similar module.
Re: Logical operations on arrays
by Kenosis (Priest) on Oct 04, 2012 at 15:59 UTC

    One option is to use List::Compare:

    use strict; use warnings; use List::Compare; my @a = qw(a b c); my @b = qw(b c d); print "\@a = @a\n\@b = @b\n\n"; print '@a AND @b = ', arrayANDCompare( \@a, \@b ), "\n\n"; print '@a OR @b = ', arrayORCompare( \@a, \@b ); sub arrayANDCompare { my ( $a, $b ) = @_; return List::Compare->new( $a, $b )->get_intersection; } sub arrayORCompare { my ( $a, $b ) = @_; return List::Compare->new( $a, $b )->get_union; }

    Output:

    @a = a b c @b = b c d @a AND @b = bc @a OR @b = abcd

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