#!/usr/bin/perl

use strict;
use warnings;

my @array = (3,2,1,1,1,2,3,4,6,"",5,"","",9,"","");

my @clean_array = clean(@array);
my @clean_ord_array = clean_ord(@array);

print "\nclean_array:\n";
map { print "elem: $_\n"; } @clean_array;

print "\nclean_ord_array:\n";
map { print "elem: $_\n"; } @clean_ord_array;

# clean, don't preserve order
sub clean {
    my @clean = @_;
    my @seen;
    my @cleaned;
    my %seen;
    my $i;

    for ( $i = 0 ; $i <= $#clean ; $i++ ) {
        unless ( ( defined $clean[$i] ) && ( $clean[$i] ne '' ) ) {
            splice @clean, $i, 1;
        }
    }

    @seen{@clean} = ();
    @cleaned = sort keys %seen;

    if (wantarray) {
        return @cleaned;
    }
    else {
        if ( defined($/) ) {
            return join "$/", @cleaned;
        }
        else {
            return join "\n", @cleaned;
        }
    }
}

# clean, preserve order
sub clean_ord {
    my @clean = @_;
    my $clean;
    my @seen;
    my @cleaned;
    my %seen;
    my $i;

    for ( $i = 0 ; $i <= $#clean ; $i++ ) {
        unless ( ( defined $clean[$i] ) && ( $clean[$i] ne '' ) ) {
            splice @clean, $i, 1;
        }
    }

    foreach $clean (@clean) {
        unless ( exists $seen{$clean} ) {
            push ( @cleaned, $clean );
            $seen{$clean} = 1;
        }
    }

    if (wantarray) {
        return @cleaned;
    }
    else {
        if ( defined($/) ) {
            return join "$/", @cleaned;
        }
        else {
            return join "\n", @cleaned;
        }
    }
}
[download]

The output is:

 
clean_array:
elem:
elem: 1
elem: 2
elem: 3
elem: 4
elem: 5
elem: 6
elem: 9
 
clean_ord_array:
elem: 3
elem: 2
elem: 1
elem: 4
elem: 6
elem: 5
elem:
elem: 9
[download]

But should be:

 
clean_array:
elem: 1
elem: 2
elem: 3
elem: 4
elem: 5
elem: 6
elem: 9
 
clean_ord_array:
elem: 3
elem: 2
elem: 1
elem: 4
elem: 6
elem: 5
elem: 9
[download]