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be kind and comment, especially if you downvote

levenshtein_distance() is an implementation of the iterative algorithm for the levenshtein distance (cf. http://en.wikipedia.org/wiki/Levenshtein_distance#Iterative_with_full_matrix)

levenshtein_sequence() is an attempt to retrieve one of the levenshtein paths (the one that give priority to substitution, deletion, insertion, in this order). The result is a list of tuples made of:

1. the operation ( =, -, +, * for respectively keep, delete, insert, substitute)
2. the coordinate in the first
3. and in the second string.
>>> levenshtein_sequence('saturday', 'sunday')
[('=', 0, 0), ('-', 1, 0), ('-', 2, 0), ('=', 3, 1), ('*', 4, 2), ('=', 5, 3), ('=', 6, 4), ('=', 7, 5)]
>>> levenshtein_sequence('kitten', 'sitting')
[('*', 0, 0), ('=', 1, 1), ('=', 2, 2), ('=', 3, 3), ('*', 4, 4), ('=', 5, 5), ('+', 5, 6)]

This code is part of foreplays, in a plan I have to improve difflib with alternative SequenceMatchers \o/

/!\ tab indented, as usual.

Python, 85 lines
 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 #!/usr/bin/env python3 def square_list(a, b, value=0) : return [[value,] * b for j in range(a)] def arg_min(* arg_list) : arg_s = None for i, arg in enumerate(arg_list) : if i == 0 or arg < arg_s : arg_s = arg i_s = i return i_s, arg_s MODIFIED = 0 DELETED = 1 CREATED = 2 def levenshtein_distance(a, b) : """ return the levenshtein distance between two strings of list of """ len_a = len(a) len_b = len(b) d = square_list(len_a+1, len_b+1) for i in range(1, len_a+1) : d[i][0] = i for j in range(1, len_b+1) : d[0][j] = j for j in range(1, len_b+1) : for i in range(1, len_a+1) : if a[i-1] == b[j-1] : d[i][j] = d[i-1][j-1] else : d[i][j] = min(d[i-1][j], d[i][j-1], d[i-1][j-1]) + 1 return d[-1][-1] def levenshtein_sequence(a, b) : """ return an explicit list of difference between a and b """ len_a = len(a) len_b = len(b) s = list() d = square_list(len_a+1, len_b+1) for i in range(1, len_a+1) : d[i][0] = i for j in range(1, len_b+1) : d[0][j] = j for j in range(1, len_b+1) : for i in range(1, len_a+1) : if a[i-1] == b[j-1] : d[i][j] = d[i-1][j-1] else : d[i][j] = min(d[i-1][j], d[i][j-1], d[i-1][j-1]) + 1 prev_i, prev_j = i, j while i > 0 and j > 0 : if i == 1 and j == 1 : if prev_i != i and prev_j != j : u = MODIFIED elif prev_i == i : u = CREATED elif prev_j == j : u = DELETED new_i, new_j = i-1, j-1 elif i == 1 : new_i, new_j = i, j-1 u = CREATED elif j == 1 : u = DELETED new_i, new_j = i-1, j else : u, null = arg_min(d[i-1][j-1], d[i-1][j], d[i][j-1]) new_i, new_j = i - (1,1,0)[u], j - (1,0,1)[u] op = '*-+'[u] if d[i][j] != d[new_i][new_j] else '=' s.append((op, i-1, j-1)) prev_i, prev_j = i, j i, j = new_i, new_j return list(reversed(s))
 Created by yota on Wed, 15 Jan 2014 (GPL3)

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