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fix: JaroWinklerDistance of single character strings that differ in case #786

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fix: JaroWinklerDistance of single character strings that differ in case #786

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5 changes: 3 additions & 2 deletions lib/natural/distance/jaro-winkler_distance.js
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Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,8 @@ function distance (s1, s2) {
return 0
}

const matchWindow = (Math.floor(Math.max(s1.length, s2.length) / 2.0)) - 1
// The window is negative for strings of length 1, so clamp it to 0
const matchWindow = Math.max(0, (Math.floor(Math.max(s1.length, s2.length) / 2.0)) - 1)
const matches1 = new Array(s1.length)
const matches2 = new Array(s2.length)
let m = 0 // number of matches
Expand Down Expand Up @@ -115,7 +116,7 @@ function JaroWinklerDistance (s1, s2, options = {}) {
const jaro = (options.dj === undefined) ? distance(s1, s2) : options.dj
const p = 0.1 // default scaling factor
let l = 0 // length of the matching prefix
while (s1[l] === s2[l] && l < 4) {
while (l < 4 && l < s1.length && l < s2.length && s1[l] === s2[l]) {
l++
}

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14 changes: 14 additions & 0 deletions spec/jaro-winkler_spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,20 @@ describe('jaro-winkler', function () {
expect(approxEql(JaroWinklerDistance('MARTHA', 'MARHTA', { ignoreCase: true }), 0.96111)).toBeTruthy()
expect(JaroWinklerDistance('abcd', 'ABCD', { ignoreCase: true })).toBe(1)
})

it('should handle strings of length 1', function () {
expect(JaroWinklerDistance('a', 'a', {})).toBe(1)
expect(JaroWinklerDistance('a', 'b', {})).toBe(0)
expect(JaroWinklerDistance('A', 'a', {})).toBe(0)
expect(JaroWinklerDistance('A', 'a', { ignoreCase: true })).toBe(1)
expect(JaroWinklerDistance('a', 'A', { ignoreCase: true })).toBe(1)
expect(JaroWinklerDistance('A', 'b', { ignoreCase: true })).toBe(0)
})

it('should not count a matching prefix longer than the strings', function () {
// Both strings are 2 characters long, so the matching prefix is at most 2: 0.5 + 2 * 0.1 * (1 - 0.5)
expect(approxEql(JaroWinklerDistance('Ab', 'aB', { ignoreCase: true, dj: 0.5 }), 0.6)).toBeTruthy()
})
it('should not fail while passing no options', function () {
expect(approxEql(JaroWinklerDistance('check', 'chakk'), 0.78666)).toBeTruthy()
})
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