# Javascript Damerau Levenshtein Algorithim

November 2012 · 2 minute read

The Damerau Levenshtein algorithim calculates a distance between two words in the same way that basic Levenshtein does but adds transpositions to the set of operations that it uses to calculate distance. This makes it much more reliable at finding similiar or alternate spellings of words.

I was doing some nodejs work lately and needed such a function to clean up one of my datasets and so I ported this version from C# to Javascript.

Enjoy!

``````function damerauLevenshteinDistance(source, target) {
if (!source || source.length === 0)
if (!target || target.length === 0)
return 0;
else
return target.length;
else if (!target)
return source.length;

var sourceLength = source.length;
var targetLength = target.length;
var score = [];

var INF = sourceLength + targetLength;
score = [INF];
for (var i=0 ; i <= sourceLength ; i++) { score[i + 1] = []; score[i + 1] = i; score[i + 1] = INF; }
for (var i=0 ; i <= targetLength ; i++) { score[i + 1] = i; score[i + 1] = INF; }

var sd = {};
var combinedStrings = source + target;
var combinedStringsLength = combinedStrings.length;
for(var i=0 ; i < combinedStringsLength ; i++) {
var letter = combinedStrings[i];
if (!sd.hasOwnProperty(letter))
sd[letter] = 0;
}

for (var i=1 ; i <= sourceLength ; i++) {
var DB = 0;
for (var j=1 ; j <= targetLength ; j++) {
var i1 = sd[target[j - 1]];
var j1 = DB;

if (source[i - 1] == target[j - 1]) {
score[i + 1][j + 1] = score[i][j];
DB = j;
}
else
score[i + 1][j + 1] = Math.min(score[i][j], Math.min(score[i + 1][j], score[i][j + 1])) + 1;

score[i + 1][j + 1] = Math.min(score[i + 1][j + 1], score[i1][j1] + (i - i1 - 1) + 1 + (j - j1 - 1));
}
sd[source[i - 1]] = i;
}
return score[sourceLength + 1][targetLength + 1];
}
``````