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package com.rockymadden.stringmetric.similarity
import com.rockymadden.stringmetric.{StringMetric, StringFilter}
import com.rockymadden.stringmetric.tokenization.NGramTokenizer
/* An implementation of the Jaccard metric. */
class JaccardMetric extends StringMetric[Int, Double] { this: StringFilter =>
final override def compare(charArray1: Array[Char], charArray2: Array[Char])(implicit n: Int): Option[Double] = {
if (n <= 0) throw new IllegalArgumentException("Expected valid n.")
val fca1 = filter(charArray1)
lazy val fca2 = filter(charArray2)
if (fca1.length < n || fca2.length < n) None // Because length is less than n, it is not possible to compare.
else if (fca1.sameElements(fca2)) Some(1d)
else NGramTokenizer.tokenize(fca1)(n).flatMap { ca1bg =>
NGramTokenizer.tokenize(fca2)(n).map { ca2bg =>
val i = (ca1bg.map(_.mkString) intersect ca2bg.map(_.mkString)).length
i.toDouble / (ca1bg.length + ca2bg.length - i)
}
}
}
final override def compare(string1: String, string2: String)(implicit n: Int): Option[Double] =
compare(string1.toCharArray, string2.toCharArray)(n: Int)
}
object JaccardMetric {
private lazy val self = apply()
def apply(): JaccardMetric = new JaccardMetric with StringFilter
def compare(charArray1: Array[Char], charArray2: Array[Char])(n: Int) = self.compare(charArray1, charArray2)(n)
def compare(string1: String, string2: String)(n: Int) = self.compare(string1, string2)(n)
}
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