2021-10-01 03:27:07 -05:00
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/* The Sørensen–Dice coefficient is a statistic used to gauge the similarity of two samples.
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* Applied to strings, it can give you a value between 0 and 1 (included) which tells you how similar they are.
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2021-10-28 15:37:43 +05:30
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* Dice coefficient is calculated by comparing the bigrams of both strings,
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2021-10-01 03:27:07 -05:00
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* a bigram is a substring of the string of length 2.
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* read more: https://en.wikipedia.org/wiki/S%C3%B8rensen%E2%80%93Dice_coefficient
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*/
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// Time complexity: O(m + n), m and n being the sizes of string A and string B
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// Find the bistrings of a string and return a hashmap (key => bistring, value => count)
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2023-10-03 23:08:19 +02:00
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function mapBigrams(string) {
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2021-10-01 03:27:07 -05:00
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const bigrams = new Map()
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for (let i = 0; i < string.length - 1; i++) {
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const bigram = string.substring(i, i + 2)
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const count = bigrams.get(bigram)
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bigrams.set(bigram, (count || 0) + 1)
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}
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return bigrams
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}
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// Calculate the number of common bigrams between a map of bigrams and a string
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2023-10-03 23:08:19 +02:00
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function countCommonBigrams(bigrams, string) {
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2021-10-01 03:27:07 -05:00
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let count = 0
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for (let i = 0; i < string.length - 1; i++) {
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const bigram = string.substring(i, i + 2)
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if (bigrams.has(bigram)) count++
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}
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return count
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}
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// Calculate Dice coeff of 2 strings
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2023-10-03 23:08:19 +02:00
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function diceCoefficient(stringA, stringB) {
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2021-10-01 03:27:07 -05:00
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if (stringA === stringB) return 1
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else if (stringA.length < 2 || stringB.length < 2) return 0
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const bigramsA = mapBigrams(stringA)
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const lengthA = stringA.length - 1
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const lengthB = stringB.length - 1
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let dice = (2 * countCommonBigrams(bigramsA, stringB)) / (lengthA + lengthB)
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// cut 0.xxxxxx to 0.xx for simplicity
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dice = Math.floor(dice * 100) / 100
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return dice
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}
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2021-10-11 14:07:10 +02:00
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2021-10-01 03:27:07 -05:00
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export { diceCoefficient }
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