From c1c6c2228a446ed42bf4382d4703309865f6dc54 Mon Sep 17 00:00:00 2001
From: Xiangrui Meng <meng@databricks.com>
Date: Thu, 13 Mar 2014 13:47:11 -0700
Subject: [PATCH] add AreaUnderCurve

---
 .../mllib/evaluation/AreaUnderCurve.scala     | 55 +++++++++++++++++++
 .../evaluation/AreaUnderCurveSuite.scala      | 47 ++++++++++++++++
 2 files changed, 102 insertions(+)
 create mode 100644 mllib/src/main/scala/org/apache/spark/mllib/evaluation/AreaUnderCurve.scala
 create mode 100644 mllib/src/test/scala/org/apache/spark/mllib/evaluation/AreaUnderCurveSuite.scala

diff --git a/mllib/src/main/scala/org/apache/spark/mllib/evaluation/AreaUnderCurve.scala b/mllib/src/main/scala/org/apache/spark/mllib/evaluation/AreaUnderCurve.scala
new file mode 100644
index 0000000000000..8d014c9f38726
--- /dev/null
+++ b/mllib/src/main/scala/org/apache/spark/mllib/evaluation/AreaUnderCurve.scala
@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.mllib.evaluation
+
+import org.apache.spark.rdd.RDD
+
+/**
+ * Computes the area under the curve (AUC) using the trapezoidal rule.
+ */
+object AreaUnderCurve {
+
+  private def trapezoid(points: Array[(Double, Double)]): Double = {
+    require(points.length == 2)
+    (points(1)._1 - points(0)._1) * (points(1)._2 + points(0)._2 ) / 2.0
+  }
+
+  /**
+   * Returns the area under the given curve.
+   *
+   * @param curve a RDD of ordered 2D points stored in pairs representing a curve
+   */
+  def of(curve: RDD[(Double, Double)]): Double = {
+    curve.sliding(2).aggregate(0.0)(
+      seqOp = (auc: Double, points: Array[(Double, Double)]) => auc + trapezoid(points),
+      combOp = (_ + _)
+    )
+  }
+
+  /**
+   * Returns the area under the given curve.
+   *
+   * @param curve an iterable of ordered 2D points stored in pairs representing a curve
+   */
+  def of(curve: Iterable[(Double, Double)]): Double = {
+    curve.sliding(2).map(_.toArray).filter(_.size == 2).aggregate(0.0)(
+      seqop = (auc: Double, points: Array[(Double, Double)]) => auc + trapezoid(points),
+      combop = (_ + _)
+    )
+  }
+}
diff --git a/mllib/src/test/scala/org/apache/spark/mllib/evaluation/AreaUnderCurveSuite.scala b/mllib/src/test/scala/org/apache/spark/mllib/evaluation/AreaUnderCurveSuite.scala
new file mode 100644
index 0000000000000..78dd65c1721b6
--- /dev/null
+++ b/mllib/src/test/scala/org/apache/spark/mllib/evaluation/AreaUnderCurveSuite.scala
@@ -0,0 +1,47 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.mllib.evaluation
+
+import org.scalatest.FunSuite
+
+import org.apache.spark.mllib.util.LocalSparkContext
+
+class AreaUnderCurveSuite extends FunSuite with LocalSparkContext {
+
+  test("auc computation") {
+    val curve = Seq((0.0, 0.0), (1.0, 1.0), (2.0, 3.0), (3.0, 0.0))
+    val auc = 4.0
+    assert(AreaUnderCurve.of(curve) === auc)
+    val rddCurve = sc.parallelize(curve, 2)
+    assert(AreaUnderCurve.of(rddCurve) == auc)
+  }
+
+  test("auc of an empty curve") {
+    val curve = Seq.empty[(Double, Double)]
+    assert(AreaUnderCurve.of(curve) === 0.0)
+    val rddCurve = sc.parallelize(curve, 2)
+    assert(AreaUnderCurve.of(rddCurve) === 0.0)
+  }
+
+  test("auc of a curve with a single point") {
+    val curve = Seq((1.0, 1.0))
+    assert(AreaUnderCurve.of(curve) === 0.0)
+    val rddCurve = sc.parallelize(curve, 2)
+    assert(AreaUnderCurve.of(rddCurve) === 0.0)
+  }
+}