Question

use Modern::Perl;
use Algorithm::Permute;
use List::AllUtils qw/uniq/;

find_perms(1151);

sub find_perms { 
  my ($value) = @_;
  my @others;
  my @digits = split(//, $value);

  my $perm = Algorithm::Permute->new( \@digits );

  while (my @next = $perm->next()) { 
    my $number = join('', @next);
    push @others, $number;
  }
  @others = sort uniq @others;

  # this one works correctly
  # @others = sort ( uniq( @others ));

  say "FOUND @others";
}

Output:
FOUND 1115 1115 1115 1115 1115 1115 1151 1151 1151 1151 1151 1151 1511 1511 1511 1511 1511 1511 5111 5111 5111 5111 5111 5111

Hi,

After discovering out that Algorithm::Permute is producing duplicates, most likely due to the amount of ‘1’s in “1151” i decided to use uniq. However using sort uniq without the parenthesis doesn’t produce expected results. But sort(uniq(@x)) does. What gives?

Answer 1

perldoc -f sort lists three syntaxes for the sort function:

sort SUBNAME LIST
sort BLOCK LIST
sort LIST

sort uniq @others matches the sort SUBNAME LIST syntax of sort. It expects uniq to be a function that compares the global variables $a and $b, and returns <0, 0, or >0 to indicate the relative ordering of $a and $b.

It looks like you were expecting and wanting the sort LIST syntax, which is what you get when you say one of

sort(uniq(@others))
sort(uniq @others)