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fix(distance): keep Damerau-Levenshtein symmetric for repeated characters #778

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fix(distance): keep Damerau-Levenshtein symmetric for repeated characters #778

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13 changes: 8 additions & 5 deletions lib/natural/distance/levenshtein_distance.js
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Original file line number Diff line number Diff line change
Expand Up @@ -218,13 +218,16 @@ function levenshteinDistance (source, target, options) {

distanceMatrix[row][column] = { cost: minCostParent.cost, parentCell: minCostParent.coordinates }

if (isUnrestrictedDamerau) {
lastRowMap[sourceElement] = row
if (sourceElement === targetElement) {
lastColMatch = column
}
if (isUnrestrictedDamerau && sourceElement === targetElement) {
lastColMatch = column
}
}
// da[c]: last row in which source character c occurred. Update after the
// inner loop so the transposition lookup only references earlier rows; the
// per-column update gave wrong distances for repeated characters (issue #757).
if (isUnrestrictedDamerau) {
lastRowMap[source[row - 1]] = row
}
}

if (!options.search) {
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5 changes: 5 additions & 0 deletions spec/damerau_levenshtein_spec.ts
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Expand Up @@ -25,6 +25,11 @@ describe('DamerauLevenshtein', function () {
expect(DamerauLevenshteinDistance('CA', 'ABC')).toBe(2)
expect(DamerauLevenshteinDistance('a cat', 'a abct')).toBe(2)
})

it('should stay symmetric for strings with repeated characters (issue #757)', function () {
expect(DamerauLevenshteinDistance('0,1,10,11', '0,11,110,111')).toBe(3)
expect(DamerauLevenshteinDistance('0,11,110,111', '0,1,10,11')).toBe(3)
})
})

describe('options.restricted = true', function () {
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