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How to find and remove duplicate elements from an array?

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Contributed by psmail on Jun 21, 2001 at 23:04 UTC
Q&A  > arrays


Answer: How to find and remove duplicate elements from an array?
contributed by japhy

This is a FAQ, because it's so frequently asked. See How can I remove duplicate elements from a list or array?

Answer: How to find and remove duplicate elements from an array?
contributed by jdporter

The answers in the FAQ don't modify the array in-place. In case that's what you need, you can do the following:

my @a = qw( a a b c c c d e f e f e a f g h h h ); my %seen; for ( my $i = 0; $i <= $#a ; ) { splice @a, --$i, 1 if $seen{$a[$i++]}++; } print "@a\n";
This can be wrapped in a sub like so:
sub remove_duplicates(\@) { my $ar = shift; my %seen; for ( my $i = 0; $i <= $#{$ar} ; ) { splice @$ar, --$i, 1 if $seen{$ar->[$i++]}++; } } my @a = qw( a a b c c c d e f e f e a f g h h h ); remove_duplicates( @a ); print "@a\n";
Answer: How to find and remove duplicate elements from an array?
contributed by pvaldes

use Array::Utils::unique:

use strict; use Array::Utils qw(:all); my @array = qw( a b c d c d e f g g g g g f); my @unique_array = unique(@array); print "@unique_array\n"; __END__ prints: e c a g b d f
In fact, the code for sub unique is a one liner; you could just hork and use it verbatim:
@unique_array = keys %{{map { $_ => undef } @array }};
There's also the (arguably more standard) List::MoreUtils::uniq.

Its code is nearly a one-liner. Copying it would look like this:

my %seen; @unique_array = grep { not $seen{$_}++ } @array;
Answer: How to find and remove duplicate elements from an array?
contributed by simmisam

A solution that uses Tie::IxHash, a tie-able which preserves the keys of a hash in the order in which they were added:

use Tie::IxHash; sub removeDuplicates { tie my %tempHash, 'Tie::IxHash'; $tempHash{$_}++ for @_; keys %tempHash; } # Remove repeated elements from an array my @array1 = qw( 4 3 7 4 3 8 9 12 23 43 23 12 ); my @uniqArray = removeDuplicates( @array1 ); print "@uniqArray";

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