1 files changed, 67 insertions, 0 deletions
diff --git a/per_sentence_bleu b/per_sentence_bleu
new file mode 100755
index 0000000..f024e74
--- /dev/null
+++ b/per_sentence_bleu
@@ -0,0 +1,67 @@
+#!/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/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
+