Method: String#edit_distance
- Defined in:
-
lib/core/facets/string/edit_distance.rb,
lib/core/facets/string/edit_distance.rb
Levenshtein distance algorithm implementation for Ruby, with UTF-8 support.
The Levenshtein distance is a measure of how similar two strings s and t are, calculated as the number of deletions/insertions/substitutions needed to transform s into t. The greater the distance, the more the strings differ.
The Levenshtein distance is also sometimes referred to as the easier-to-pronounce-and-spell ‘edit distance’.
Calculate the Levenshtein distance between two strings self
and str2
. self
and str2
should be ASCII, UTF-8, or a one-byte-per character encoding such as ISO-8859-*.
The strings will be treated as UTF-8 if $KCODE is set appropriately (i.e. ‘u’). Otherwise, the comparison will be performed byte-by-byte. There is no specific support for Shift-JIS or EUC strings.
When using Unicode text, be aware that this algorithm does not perform normalisation. If there is a possibility of different normalised forms being used, normalisation should be performed beforehand.
CREDIT: Paul Battley
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# File 'lib/core/facets/string/edit_distance.rb', line 25 def edit_distance(str2) str1 = self if $KCODE =~ /^U/i unpack_rule = 'U*' else unpack_rule = 'C*' end s = str1.unpack(unpack_rule) t = str2.unpack(unpack_rule) n = s.length m = t.length return m if (0 == n) return n if (0 == m) d = (0..m).to_a x = nil (0...n).each do |i| e = i+1 (0...m).each do |j| cost = (s[i] == t[j]) ? 0 : 1 x = [ d[j+1] + 1, # insertion e + 1, # deletion d[j] + cost # substitution ].min d[j] = e e = x end d[m] = x end return x end |