1 files changed, 27 insertions, 0 deletions
diff --git a/core/src/main/scala/com/rockymadden/stringmetric/similarity/DiceSorensenMetric.scala b/core/src/main/scala/com/rockymadden/stringmetric/similarity/DiceSorensenMetric.scala
new file mode 100755
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--- /dev/null
+++ b/core/src/main/scala/com/rockymadden/stringmetric/similarity/DiceSorensenMetric.scala
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+package com.rockymadden.stringmetric.similarity
+
+import com.rockymadden.stringmetric.Metric.StringMetric
+
+/**
+ * An implementation of the Dice/Sorensen metric. This implementation differs in that n-gram size is required.
+ * Traditionally, the algorithm uses bigrams.
+ */
+final case class DiceSorensenMetric(n: Int) extends StringMetric[Double] {
+	import com.rockymadden.stringmetric.Tokenize.NGramTokenizer
+	import com.rockymadden.stringmetric.MatchTuple
+
+	override def compare(a: Array[Char], b: Array[Char]): Option[Double] =
+		if (n <= 0 || 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 ms = scoreMatches(ca1bg.map(_.mkString), ca2bg.map(_.mkString))
+
+				(2d * ms) / (ca1bg.length + ca2bg.length)
+			}
+		}
+
+	override def compare(a: String, b: String): Option[Double] = compare(a.toCharArray, b.toCharArray)
+
+	private val scoreMatches: (MatchTuple[String] => Int) = (mt) => mt._1.intersect(mt._2).length
+}