Created LevenshteinMetric, spec, and command.

2 files changed, 90 insertions, 0 deletions

diff --git a/core/source/core/scala/org/hashtree/stringmetric/LevenshteinMetric.scala b/core/source/core/scala/org/hashtree/stringmetric/LevenshteinMetric.scala
new file mode 100755
index 0000000..9465c66
--- /dev/null
+++ b/core/source/core/scala/org/hashtree/stringmetric/LevenshteinMetric.scala
@@ -0,0 +1,60 @@
+package org.hashtree.stringmetric
+
+import scala.math
+
+/** An implementation of the Levenshtein [[org.hashtree.stringmetric.StringMetric]]. */
+object LevenshteinMetric extends StringMetric {
+	implicit val stringCleaner = new StringCleanerDelegate with CaseStringCleaner
+
+	override def compare(charArray1: Array[Char], charArray2: Array[Char])(implicit stringCleaner: StringCleaner): Option[Int] = {
+		val ca1 = stringCleaner.clean(charArray1)
+		val ca2 = stringCleaner.clean(charArray2)
+
+		if (ca1.length == 0 && ca2.length == 0)
+			None
+		else {
+			val levenshteinMemoize = Memoize.Y(levenshtein)
+
+			Some(levenshteinMemoize(ca1, ca2))
+		}
+	}
+
+	override def compare(string1: String, string2: String)(implicit stringCleaner: StringCleaner): Option[Int] = {
+		compare(
+			stringCleaner.clean(string1.toCharArray),
+			stringCleaner.clean(string2.toCharArray)
+		)(new StringCleanerDelegate)
+	}
+
+	private[this] def levenshtein(f: CompareTuple => Int)(ct: CompareTuple): Int = {
+		if (ct._1.length == 0)
+			ct._2.length
+		else if (ct._2.length == 0)
+			ct._1.length
+		else {
+			math.min(
+				math.min(
+					f(ct._1.tail, ct._2) + 1,
+					f(ct._1, ct._2.tail) + 1
+				),
+				f(ct._1.tail, ct._2.tail) + (if (ct._1.head != ct._2.head) 1 else 0)
+			)
+		}
+	}
+
+	private[this] final class Memoize[-T, +R](f: T => R) extends (T => R) {
+		private[this] val map = scala.collection.mutable.Map[T, R]()
+
+		def apply(k: T): R = map.getOrElseUpdate(k, f(k))
+	}
+
+	private[this] object Memoize {
+		def apply[T, R](f: T => R) = new Memoize(f)
+
+		def Y[T, R](f: (T => R) => T => R): (T => R) = {
+			lazy val yf: T => R = Memoize(f(yf)(_))
+
+			yf
+		}
+	}
+}
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diff --git a/core/source/test/scala/org/hashtree/stringmetric/LevenshteinMetricSpec.scala b/core/source/test/scala/org/hashtree/stringmetric/LevenshteinMetricSpec.scala
new file mode 100755
index 0000000..01c9082
--- /dev/null
+++ b/core/source/test/scala/org/hashtree/stringmetric/LevenshteinMetricSpec.scala
@@ -0,0 +1,30 @@
+package org.hashtree.stringmetric
+
+import org.hashtree.stringmetric.LevenshteinMetric.stringCleaner
+import org.junit.runner.RunWith
+import org.scalatest.junit.JUnitRunner
+
+@RunWith(classOf[JUnitRunner])
+final class LevenshteinMetricSpec extends ScalaTest {
+	"LevenshteinMetric" should provide {
+		"compare method" when passed {
+			"valid arguments" should returns {
+				"Int indicating distance" in {
+					LevenshteinMetric.compare("", "").isDefined should be (false)
+
+					LevenshteinMetric.compare("abc", "").get should be (3)
+					LevenshteinMetric.compare("", "xyz").get should be (3)
+					LevenshteinMetric.compare("abc", "abc").get should be (0)
+					LevenshteinMetric.compare("abc", "xyz").get should be (3)
+					LevenshteinMetric.compare("abc", "a").get should be (2)
+					LevenshteinMetric.compare("a", "abc").get should be (2)
+					LevenshteinMetric.compare("abc", "c").get should be (2)
+					LevenshteinMetric.compare("c", "abc").get should be (2)
+
+					LevenshteinMetric.compare("kitten", "sitting").get should be (3)
+					LevenshteinMetric.compare("drake", "cake").get should be (2)
+				}
+			}
+		}
+	}
+}
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