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

[Anonymous Monk]

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

Originally posted as a Categorized Question.

[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.

[knobunc]

This is fine for some cases, but it does not preserve the ordering of the elements in the array. The origial poster did not indicate if they cared. Anyway, as IO pointed out, the node How can I extract just the unique elements of an array? discusses several methods for dealing with this depending upon the data that you are dealing with.

-ben

[I0]

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

[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.

[nudge]

use List::MoreUtils qw(uniq);

my @list = (1,1,2,3,3,4);
print join( ',', uniq(@list) );

[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{ ! $seen{$_} ++} @_;}
}

[halley]

Okay, that's a really bad idea. You're naming a sub suggestively and then offering two OPPOSITE functionalities.

You're expecting the caller to choose the desired action with an UNRELATED and NON-MNEMONIC distinction like ref($_[0]) vs not ref($_[0]).

What if you send a plain @array1 and the zeroth element is an array ref? You might want to get a unique set of array refs, but this function's not going to help there.

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