Created DiceSorensen metric, spec, and command.

2 files changed, 79 insertions, 0 deletions

diff --git a/core/source/core/scala/org/hashtree/stringmetric/distance/DiceSorensenMetric.scala b/core/source/core/scala/org/hashtree/stringmetric/distance/DiceSorensenMetric.scala
new file mode 100755
index 0000000..efec67c
--- /dev/null
+++ b/core/source/core/scala/org/hashtree/stringmetric/distance/DiceSorensenMetric.scala
@@ -0,0 +1,44 @@
+package org.hashtree.stringmetric.distance
+
+import org.hashtree.stringmetric.{ CompareTuple, MatchTuple, StringCleaner, StringCleanerDelegate, StringMetric }
+import scala.annotation.tailrec
+
+/** An implementation of the Dice, and Sorensen, [[org.hashtree.stringmetric.StringMetric]]. */
+object DiceSorensenMetric extends StringMetric {
+	override def compare(charArray1: Array[Char], charArray2: Array[Char])(implicit stringCleaner: StringCleaner): Option[Float] = {
+		val ca1 = stringCleaner.clean(charArray1)
+		val ca2 = stringCleaner.clean(charArray2)
+
+		if (ca1.length == 0 || ca2.length == 0) None
+		else {
+			val b = bigrams(ca1, ca2)
+			val ms = scoreMatches(b)
+
+			Some((2f * ms) / (b._1.length + b._2.length))
+		}
+	}
+
+	override def compare(string1: String, string2: String)(implicit stringCleaner: StringCleaner): Option[Float] = {
+		if (string1.length > 0 && string1.length == string2.length && string1 == string2) Some(1f)
+		else
+			compare(
+				stringCleaner.clean(string1.toCharArray),
+				stringCleaner.clean(string2.toCharArray)
+			)(new StringCleanerDelegate)
+	}
+
+	private[this] def bigrams(ct: CompareTuple[Char]): MatchTuple[String] = {
+		@tailrec
+		def set(ca: Array[Char], sa: Array[String]): Array[String] = {
+			if (ca.length <= 1) sa
+			else
+				set(ca.tail, sa :+ "" + ca.head + ca.tail.head)
+		}
+
+		(set(ct._1, Array.empty[String]), set(ct._2, Array.empty[String]))
+	}
+
+	private[this] def scoreMatches(mt: MatchTuple[String]) = {
+		mt._1.intersect(mt._2).length
+	}
+}
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diff --git a/core/source/test/scala/org/hashtree/stringmetric/distance/DiceSorensenMetricSpec.scala b/core/source/test/scala/org/hashtree/stringmetric/distance/DiceSorensenMetricSpec.scala
new file mode 100755
index 0000000..d07673b
--- /dev/null
+++ b/core/source/test/scala/org/hashtree/stringmetric/distance/DiceSorensenMetricSpec.scala
@@ -0,0 +1,35 @@
+package org.hashtree.stringmetric.distance
+
+import org.hashtree.stringmetric.ScalaTest
+import org.junit.runner.RunWith
+import org.scalatest.junit.JUnitRunner
+
+@RunWith(classOf[JUnitRunner])
+final class DiceSorensenMetricSpec extends ScalaTest {
+	"DiceSorensenMetric" should provide {
+		"compare method" when passed {
+			"empty arguments" should returns {
+				"None" in {
+					DiceSorensenMetric.compare("", "").isDefined should be (false)
+					DiceSorensenMetric.compare("abc", "").isDefined should be (false)
+					DiceSorensenMetric.compare("", "xyz").isDefined should be (false)
+				}
+			}
+			"equal arguments" should returns {
+				"1" in {
+					DiceSorensenMetric.compare("abc", "abc").get should be (1.0f)
+				}
+			}
+			"unequal arguments" should returns {
+				"0" in {
+					DiceSorensenMetric.compare("abc", "xyz").get should be (0.0f)
+				}
+			}
+			"valid arguments" should returns {
+				"Float indicating distance" in {
+					DiceSorensenMetric.compare("night", "nacht").get should be (0.25f)
+				}
+			}
+		}
+	}
+}
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