#!/usr/bin/perl -w
use strict;

my $candidate = "it is not probable that it is the end";
my $reference = "but it is unlikely that this is the end";
my @candidate_words = split (/\W+/, $candidate);
my $candidate_count=@candidate_words;
my %cand_histogram;
my %ref_histogram;
my $valHolder="";
our $res=0;
$cand_histogram{$_}++ foreach (split(/\s+/,$candidate));
$ref_histogram{$_}++  foreach (split(/\s+/,$reference));

my %seen;
printf "%-6s %-10s %-10s %10s\n", 'Key','Candidate','Reference','MinCo
+unt';
foreach my $key ( sort {
                          $seen{$b} <=> $seen{$a} #descending word cnt
                                   or
                               $a cmp $b       #alphabetic otherwise
                       }
                  grep {!$seen{$_}++}  # each key just once,
                                       # but count 'em also!
                 (keys %cand_histogram)
                )
{
#$valHolder=$cand_histogram{$key};
$valHolder=0;
if($cand_histogram{$key} && $ref_histogram{$key}){
$valHolder=$cand_histogram{$key};
if($cand_histogram{$key} >= $ref_histogram{$key}){
$valHolder=$ref_histogram{$key};
}
}
$res+=$valHolder;
printf "%-6s %-10s %-10s %10s\n", $key,
$cand_histogram{$key}||='0',
$ref_histogram{$key} ||='0',$valHolder;
}
my $BS=$res/$candidate_count;
print "The calculated bleu Score is:$BS\n";
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Here i have computed the similarity score between two sentences by taking unigrams(i.e individual words from sentences).

Now, i want to turn this same script to do the same computation but with n-gram(with n=3 i.e taking three words together through out the computation).

for eg. in unigram computation if i have a sentence "it is not probably that it is the end". then in n-gram words should be in the form

it is not
is not probably
not probably that
that it is
it is the
is the end
[download]

In this way i want to compute the similarity score between the two sentences.. any help please Thanks..

Key    Candidate  Reference    MinCount
end    1          1                   1
is     2          2                   2
it     2          1                   1
not    1          0                   0
probable 1          0                   0
that   1          1                   1
the    1          1                   1
The calculated bleu Score is:0.666666666666667
[download]