init

BLEU.py

@@ -0,0 +1,30 @@
+import numpy as np
+from collections import Counter
+
+
+def BLEU(references, generated, max_grams=4, weights=None):
+    ref_list = [ref.lower().split(" ") for ref in references]
+    gen = generated.lower().split(" ")
+    cpn = np.empty((max_grams,), dtype=np.float32)
+    for n in range(1, max_grams+1):
+        gen_gram = [" ".join(gen[i:i+n]) for i in range(0, len(gen)-n+1)]
+        refs_gram = [[" ".join(ref[i:i+n]) for i in range(0, len(ref)-n+1)] for ref in ref_list]
+        g_counter = Counter(gen_gram)
+        r_counters = [Counter(ref_gram) for ref_gram in refs_gram]
+        count_clip = 0
+        for k, v in g_counter.items():
+            count_clip += min(v, max([r.get(k, 0) for r in r_counters]))
+        cpn[n-1] = count_clip/sum(g_counter.values())
+
+    ls = len(gen)
+    lc = max([len(ref) for ref in ref_list])
+    brevity_penalty = 1 if lc > ls else np.exp(1-ls/lc)
+
+    if weights is None:
+        weights = np.ones_like(cpn)
+    bleu = brevity_penalty * np.exp(np.mean(weights * np.log(cpn)))
+    return bleu
+
+
+bleu = BLEU(["The cat is on the mat", "There is a cat on the mat"], "The cat is on the mat", 3)
+print(bleu)