WER calculation

source-code/Pseudocode/WER-calculation/wer.py

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+#!/usr/bin/env python
+
+def wer(r, h):
+    """
+        Calculation of WER with Levenshtein distance.
+        Works only for iterables up to 254 elements (uint8).
+        O(nm) time ans space complexity.
+
+        >>> wer("who is there".split(), "is there".split()) 
+        1
+        >>> wer("who is there".split(), "".split()) 
+        3
+        >>> wer("".split(), "who is there".split()) 
+        3
+    """
+    # initialisation
+    import numpy
+    d = numpy.zeros((len(r)+1)*(len(h)+1), dtype=numpy.uint8)
+    d = d.reshape((len(r)+1, len(h)+1))
+    for i in range(len(r)+1):
+        for j in range(len(h)+1):
+            if i == 0:
+                d[0][j] = j
+            elif j == 0:
+                d[i][0] = i
+
+    # computation
+    for i in range(1, len(r)+1):
+        for j in range(1, len(h)+1):
+            if r[i-1] == h[j-1]:
+                d[i][j] = d[i-1][j-1]
+            else:
+                substitution = d[i-1][j-1] + 1
+                insertion    = d[i][j-1] + 1
+                deletion     = d[i-1][j] + 1
+                d[i][j] = min(substitution, insertion, deletion)
+
+    return d[len(r)][len(h)]
+
+if __name__ == "__main__":
+    import doctest
+    doctest.testmod()