Source Code for Module nltk.metrics.windowdiff'

 1  # Natural Language Toolkit: Windowdiff 
 2  # 
 3  # Copyright (C) 2001-2011 NLTK Project 
 4  # Author: Edward Loper <edloper@gradient.cis.upenn.edu> 
 5  #         Steven Bird <sb@csse.unimelb.edu.au> 
 6  # URL: <http://www.nltk.org/> 
 7  # For license information, see LICENSE.TXT 
 8   
 9  ########################################################################## 
10  # Windowdiff 
11  # Pevzner, L., and Hearst, M., A Critique and Improvement of 
12  #   an Evaluation Metric for Text Segmentation, 
13  # Computational Linguistics,, 28 (1), March 2002, pp. 19-36 
14  ########################################################################## 
15   
16 -def windowdiff(seg1, seg2, k, boundary="1"): 
17      """ 
18      Compute the windowdiff score for a pair of segmentations.  A segmentation is any sequence 
19      over a vocabulary of two items (e.g. "0", "1"), where the specified boundary value is used 
20      to mark the edge of a segmentation. 
21       
22      >>> s1 = "00000010000000001000000" 
23      >>> s2 = "00000001000000010000000" 
24      >>> s3 = "00010000000000000001000" 
25      >>> windowdiff(s1, s1, 3) 
26      0 
27      >>> windowdiff(s1, s2, 3) 
28      4 
29      >>> windowdiff(s2, s3, 3) 
30      16 
31   
32      @param seg1: a segmentation 
33      @type seg1: C{string} or C{list} 
34      @param seg2: a segmentation 
35      @type seg2: C{string} or C{list} 
36      @param k: window width 
37      @type k: C{int} 
38      @param boundary: boundary value 
39      @type boundary: C{string} or C{int} or C{bool} 
40      @rtype: C{int} 
41      """ 
42   
43      if len(seg1) != len(seg2): 
44          raise ValueError, "Segmentations have unequal length" 
45      wd = 0 
46      for i in range(len(seg1) - k): 
47          wd += abs(seg1[i:i+k+1].count(boundary) - seg2[i:i+k+1].count(boundary)) 
48      return wd 
49   
50 -def demo(): 
51      s1 = "00000010000000001000000" 
52      s2 = "00000001000000010000000" 
53      s3 = "00010000000000000001000" 
54      print "s1:", s1 
55      print "s2:", s2 
56      print "s3:", s3 
57   
58      print "windowdiff(s1, s1, 3) = ", windowdiff(s1, s1, 3)  
59      print "windowdiff(s1, s2, 3) = ", windowdiff(s1, s2, 3)  
60      print "windowdiff(s2, s3, 3) = ", windowdiff(s2, s3, 3) 
61