This is what I managed to do after reading the various answers. I consider a multi words unit (MWU) to be contained in a bigger one only if the sequence of words is the same (so technology process is contained in automation technology process', but 'automation process is not). I do not have other constraints I can think of.

Be aware, my code is very verbose....

use strict;
use warnings;
use Data::Dump qw/pp dd/;

my %output;

my %phrases = (
          'rendition' => '3',
          'automation' => '2',
          'saturation' => '3',
          'mass creation' => 2,
          'automation technology' => 2,
          'automation technology process' => 3,
          'technology process' => 5,
          'automation process' => 2,
           );

foreach my $keyPhrases (sort hashKeyLength (keys(%phrases))) {
    my $TermToBeRetained=1;
    print "\nWorking on * $keyPhrases *\n";
    foreach my $keyOutput (keys %output){
        print "\tChecking if * $keyPhrases * is contained in * $keyOut
+put *: ";
        if ($keyOutput =~/$keyPhrases/){
            print "Yes\n";
            $TermToBeRetained=0;
            last;
        }
        else{
            print "No!\n";
            $TermToBeRetained=1;
        }
    }
    
    if ($TermToBeRetained eq 1){
        print "Retaining $keyPhrases\n";
        $output{$keyPhrases} = $phrases{$keyPhrases};;
    }
    else{
        print "Skipping $keyPhrases\n";
    }
}

print "MY RESULT\n";
print pp \%output;

sub hashKeyLength {
    count_units_in_phrase($b) <=> count_units_in_phrase($a) || $b cmp 
+$a
}

sub count_units_in_phrase {
    my $string=shift;
    my $num; 
    $num++ while $string =~ /\S+/g;
    return $num
}

[download]

What do you think of it?

Discipuls added code tags 28 July 2018

In reply to Re: retain longest multi words units from hash by Anonymous Monk
in thread retain longest multi words units from hash by Anonymous Monk

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