Re: to select unique characters

[johngg]

The common idiom seems to be

my %seen;
my @uniq = grep { ! $seen{$_} ++ } @arr;

but using a hash slice seems to be a bit faster. I should warn that I have a chequered history with benchmarks so take this with a pinch of salt.

use strict;
use warnings;

use Benchmark q{cmpthese};

my @arr = ( q{a} .. q{z} ) x 1000;

cmpthese(
   -10,
   {
       useGrep  => sub
          {
              my %seen;
              return grep { ! $seen{$_} ++ } @arr;
          },
       useSlice => sub
          {
              my %seen;
              @seen{@arr} = ();
              return keys %seen;
          },
   });

The output.

           Rate  useGrep useSlice
useGrep  13.0/s       --     -63%
useSlice 35.2/s     172%       --

If you need to preserve the order of the array then you should use the grep method.

I hope this is of interest.

Cheers,

JohnGG