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How can I display a unique array if it contains some repeated elements

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Contributed by Anonymous Monk on Apr 28, 2001 at 03:02 UTC
Q&A  > arrays


Answer: How can I display a unique array if it contains some repeated elements
contributed by dvergin

If you mean, "How can I display an array of the unique elements of an array that contains some repeated elements", this may serve your purpose:

my @ary = qw(a b c d d e b d); my %hsh; undef @hsh{@ary}; my @ary2 = keys %hsh; print "@ary2\n";
The key here is:  undef @hsh{@ary};  which is a hash slice. The hash slice is an lvalue (that is, it is assignable). The undef is associative for each element of the slice. The effect of this is to establish a key in the hash corresponding to each array element. Except that duplicate keys just write over each other. Each key has a corresponding value of undef. Then, on the next line we just extract the (now unique) keys into a new array.
Answer: How can I display a unique array if it contains some repeated elements
contributed by I0

Are you asking How can I extract just the unique elements of an array?

Answer: How can I display a unique array if it contains some repeated elements
contributed by tadman

There is a similar technique which is slightly faster (~5-7%) on larger lists:

my %h; grep { !$h{$_}++ } @list;
The answer by dvergin is actually about 50% faster for lists smaller than ~2000 items.
Answer: How can I display a unique array if it contains some repeated elements
contributed by nudge

use List::MoreUtils qw(uniq); my @list = (1,1,2,3,3,4); print join( ',', uniq(@list) );
Answer: How can I display a unique array if it contains some repeated elements
contributed by Anonymous Monk

a sub to get both unique and not:

@array1 = (1,1,2,3,3,4); #unique print unique(@array1); #not print unique(\@array1); sub unique{ my (%seen, $array); ($array)=@_; if(@$array){return grep{$seen{$_} ++} @$array;} else{return grep{ ! $seen{$_} ++} @_;} }

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