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#!/usr/bin/env ruby
require 'trollop'
def ngrams_it(s, n, fix=false)
a = s.strip.split
a.each_with_index { |tok, i|
tok.strip!
0.upto([n-1, a.size-i-1].min) { |m|
yield a[i..i+m] if !(fix||(a[i..i+m].size>n))
}
}
end
def brevity_penalty hypothesis, reference
a = hypothesis.split; b = reference.split
return 1.0 if a.size>b.size
return Math.exp(1.0 - ((b.size.to_f+1)/a.size));
end
def per_sentence_bleu hypothesis, reference, n=4
h_ng = {}; r_ng = {}
(1).upto(n) {|i| h_ng[i] = []; r_ng[i] = []}
ngrams_it(hypothesis, n) {|i| h_ng[i.size] << i}
ngrams_it(reference, n) {|i| r_ng[i.size] << i}
m = [n, reference.split.size].min
weight = 1.0/m
add = 0.0
sum = 0
(1).upto(m) { |i|
counts_clipped = 0
counts_sum = h_ng[i].size
h_ng[i].uniq.each {|j| counts_clipped += r_ng[i].count(j)}
add = 1.0 if i >= 2
sum += weight * Math.log((counts_clipped + add)/(counts_sum + add));
}
return brevity_penalty(hypothesis, reference) * Math.exp(sum)
end
def main
opts = Trollop::options do
opt :input, "input", :type => :string, :default => '-'
opt :references, "references", :type => :string, :required => true
end
refs = File.new(opts[:references], 'r').readlines.map{|i|i.strip}
i = -1
if opts[:input] == '-'
input = STDIN
else
input = File.new opts[:input], 'r'
end
while line = input.gets
i += 1
if line.strip == ''
puts 0.0
next
end
puts per_sentence_bleu line.strip, refs[i]
end
input.close if opts[:input]!='-'
end
main
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