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package com.rockymadden.stringmetric.similarity
import com.rockymadden.stringmetric.Metric.StringMetric
final case class JaccardMetric(n: Int) extends StringMetric[Double] {
import com.rockymadden.stringmetric.tokenize.NGramTokenizer
override def compare(a: Array[Char], b: Array[Char]): Option[Double] = {
if (n <= 0) return None
if (a.length < n || b.length < n) None // Because length is less than n, it is not possible to compare.
else if (a.sameElements(b)) Some(1d)
else NGramTokenizer(n).tokenize(a).flatMap { ca1bg =>
NGramTokenizer(n).tokenize(b).map { ca2bg =>
val i = (ca1bg.map(_.mkString) intersect ca2bg.map(_.mkString)).length
i.toDouble / (ca1bg.length + ca2bg.length - i)
}
}
}
override def compare(a: String, b: String): Option[Double] = compare(a.toCharArray, b.toCharArray)
}
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