comment on

The subroutine needs some way of knowing (or, at least, guessing) whether it has been passed an array or an array reference.

First thought is to test whether the first argument is an array reference:

if (ref($_[0]) eq 'ARRAY') ...

See ref. The problem with that approach is that it won’t work if the array passed into the subroutine happens to have an array reference as its first element.

A better approach is to test whether the subroutine is called in list context:

my @array_with_duplicates = wantarray ? @_ : @{ $_[0] };

See wantarray. If the sub is called in list context (i.e., the caller is expecting it to return a list), then from the specification we can assume the array was passed in as a list. Otherwise, we assume the array was passed in as a reference.

Here is how I would solve the problem:

#! perl
use strict;
use warnings;
use Data::Dump;

my @array;

while (<DATA>)
{
    chomp;
    push @array, $_;
}

dd \@array;
    @array = clean(@array);     # or clean(\@array);
dd \@array;

sub clean
{
    my   @array_with_duplicates = wantarray ? @_ : @{$_[0]};
    my  (@array_no_duplicates, %hash);

    for (@array_with_duplicates)
    {
        unless (exists $hash{$_})
        {
            push @array_no_duplicates, $_;
            $hash{$_} = undef;
        }
    }

    return @array_no_duplicates if wantarray;
    @{ $_[0] } = @array_no_duplicates;
}

__DATA__
Frieda
Adele
Briony
Hermione
Cathy
Dorothy
Cathy
Erin
Ida
Frieda
Frieda
Gertrude
Hermione
[download]

Output:

22:14 >perl 890_SoPW.pl
[
  "Frieda",
  "Adele",
  "Briony",
  "Hermione",
  "Cathy",
  "Dorothy",
  "Cathy",
  "Erin",
  "Ida",
  "Frieda",
  "Frieda",
  "Gertrude",
  "Hermione",
]
[
  "Frieda",
  "Adele",
  "Briony",
  "Hermione",
  "Cathy",
  "Dorothy",
  "Erin",
  "Ida",
  "Gertrude",
]

22:14 >
[download]

Note: this approach does not rely on sorting the list, but outputs the no-duplicates version in its original order. The specification as given does not mention sorting.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re: How to combine these 2 subroutines in one? by Athanasius
in thread How to combine these 2 subroutines in one? by Anonymous Monk

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