The Levenshtein distance is a metric for measuring the amount of difference between two sequences (i.e., the so called edit distance). The Levenshtein distance between two sequences is given by the minimum number of operations needed to transform one sequence into the other, where an operation is an insertion, deletion, or substitution of a single element.
More information about the Levenshtein distance algorithm: en.wikipedia.org/wiki/Levenshtein_distance .
Returns the Levenshtein distance between two sequences.
The two sequences can be two strings, two arrays, or two other objects. Strings, arrays and arrays of strings are handled with optimized (very fast) C code. All other sequences are handled with generic (fast) C code.
The sequences should respond to :length and :[] and all objects in the sequences (as returned by []) should response to :==.
# File lib/levenshtein.rb, line 56 def self.distance(s1, s2, threshold=nil) s1, s2 = s2, s1 if s1.length > s2.length # s1 is the short one; s2 is the long one. # Handle some basic circumstances. return 0 if s1 == s2 return s2.length if s1.length == 0 if threshold return nil if (s2.length-s1.length) >= threshold a1, a2 = nil, nil a1, a2 = s1, s2 if s1.respond_to?(:-) and s2.respond_to?(:-) a1, a2 = s1.scan(/./), s2.scan(/./) if s1.respond_to?(:scan) and s2.respond_to?(:scan) if a1 and a2 return nil if (a1-a2).length >= threshold return nil if (a2-a1).length >= threshold end end distance_fast_or_slow(s1, s2, threshold) end
Returns the Levenshtein distance as a number between 0.0 and 1.0. It’s basically the Levenshtein distance divided by the length of the longest sequence.
# File lib/levenshtein.rb, line 28 def self.normalized_distance(s1, s2, threshold=nil) s1, s2 = s2, s1 if s1.length > s2.length # s1 is the short one; s2 is the long one. if s2.length == 0 0.0 # Since s1.length < s2.length, s1 must be empty as well. else if threshold if d = self.distance(s1, s2, (threshold*s2.length+1).to_i) d.to_f/s2.length else nil end else self.distance(s1, s2).to_f/s2.length end end end
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