Hello, ozboomer,

Your method (same method, but with or without subroutine) is clear and good. But if you have large data, it is too slow, because time complexity of the method is N*M. For every element from subset (M) you check all elements from list (N). For better time complexity you can use hashes (search: perldata).

#!/usr/bin/perl

use warnings;
use strict;
use Data::Dumper;
   
my @array = ( "APPLE", "ORANGE", "PEACH",         # Use this for the O
+RDER
           "GRAPE", "BANANA", "PINEAPPLE" );   
   
my @subset = ( "PINEAPPLE", "GRAPE", "ORANGE", "APPLE" );   # A requir
+ed subset but NOT
                                               # in the required order
   
my @results = ();                                 # The subset with it
+s elements in the 
                                               # same order as the 're
+ference' array

# ---- Method 2: Using hash

my %indexes;
my $index = 0;

map {
    $indexes{ $_ } = $index;
    $index ++; 
    } @array;

printf "  Index of element '$_' is: %d\n", $indexes{ $_ } for @subset;

my @tmp = ();
foreach my $check ( @subset ){
    my( $index ) = $indexes{ $check };
    push( @tmp, $index );
}

my @index_list = sort {$a <=> $b} @tmp;  # Sort the index values numer
+ically
@results = @array[@index_list];       # Slice the index items out of '
+@array'

print "Method 2 (uses hash):\n";
print Dumper(@results);
print "\n";
[download]

OUTPUT:

  Index of element 'PINEAPPLE' is: 5
  Index of element 'GRAPE' is: 3
  Index of element 'ORANGE' is: 1
  Index of element 'APPLE' is: 0
Method 2 (uses hash):
$VAR1 = 'APPLE';
$VAR2 = 'ORANGE';
$VAR3 = 'GRAPE';
$VAR4 = 'PINEAPPLE';
[download]