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Re: Explain the code

by gopalr (Priest)
on Jul 24, 2008 at 12:54 UTC ( #699861=note: print w/replies, xml ) Need Help??

in reply to Explain the code

This approach is merges the construction of the %seen hash with the extraction of unique elements.

1. reading elements from @array

2. If the current element ($_) and it is not in the hash (%seen), it will push into @result. Then it stored into hash(%seen). As we know hash will not allow duplicate value


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Re^2: Explain the code
by olus (Curate) on Jul 24, 2008 at 12:58 UTC

    %seen will also have the number of occurrences of every element of @a.

      How? If the array (@a) has duplicate values, hash will eliminate that.

        Noticed the ++ in !$seen{$_}++?

        perl -MData::Dumper -e '@a=(1, 2, 1, 2, 3); my @result = grep { !$seen +{$_}++ } @a; print Dumper(\%seen);' $VAR1 = { '1' => 2, '3' => 1, '2' => 2 };
        The ++ is evaluated for every item in @a, grep only checks its return value and picks (or not picks) the element based on that value.
        $seen{4} = 3 means that 4 has been seen 3 times.

        Unless I state otherwise, all my code runs with strict and warnings

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