[SPARK-8788] [ML] Add Java unit test for PCA transformer

Add Java unit test for PCA transformer

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #7184 from yanboliang/spark-8788 and squashes the following commits:

9d1a2af [Yanbo Liang] address comments
b34451f [Yanbo Liang] Add Java unit test for PCA transformer

mllib/src/test/java/org/apache/spark/ml/feature/JavaPCASuite.java

+/*
+ * 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.ml.feature;
+
+import java.io.Serializable;
+import java.util.List;
+
+import scala.Tuple2;
+
+import com.google.common.collect.Lists;
+import org.junit.After;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+
+import org.apache.spark.api.java.function.Function;
+import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.mllib.linalg.distributed.RowMatrix;
+import org.apache.spark.mllib.linalg.Matrix;
+import org.apache.spark.mllib.linalg.Vector;
+import org.apache.spark.mllib.linalg.Vectors;
+import org.apache.spark.sql.DataFrame;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.SQLContext;
+
+public class JavaPCASuite implements Serializable {
+  private transient JavaSparkContext jsc;
+  private transient SQLContext sqlContext;
+
+  @Before
+  public void setUp() {
+    jsc = new JavaSparkContext("local", "JavaPCASuite");
+    sqlContext = new SQLContext(jsc);
+  }
+
+  @After
+  public void tearDown() {
+    jsc.stop();
+    jsc = null;
+  }
+
+  public static class VectorPair implements Serializable {
+    private Vector features = Vectors.dense(0.0);
+    private Vector expected = Vectors.dense(0.0);
+
+    public void setFeatures(Vector features) {
+      this.features = features;
+    }
+
+    public Vector getFeatures() {
+      return this.features;
+    }
+
+    public void setExpected(Vector expected) {
+      this.expected = expected;
+    }
+
+    public Vector getExpected() {
+      return this.expected;
+    }
+  }
+
+  @Test
+  public void testPCA() {
+    List<Vector> points = Lists.newArrayList(
+      Vectors.sparse(5, new int[]{1, 3}, new double[]{1.0, 7.0}),
+      Vectors.dense(2.0, 0.0, 3.0, 4.0, 5.0),
+      Vectors.dense(4.0, 0.0, 0.0, 6.0, 7.0)
+    );
+    JavaRDD<Vector> dataRDD = jsc.parallelize(points, 2);
+
+    RowMatrix mat = new RowMatrix(dataRDD.rdd());
+    Matrix pc = mat.computePrincipalComponents(3);
+    JavaRDD<Vector> expected = mat.multiply(pc).rows().toJavaRDD();
+
+    JavaRDD<VectorPair> featuresExpected = dataRDD.zip(expected).map(
+      new Function<Tuple2<Vector, Vector>, VectorPair>() {
+        public VectorPair call(Tuple2<Vector, Vector> pair) {
+          VectorPair featuresExpected = new VectorPair();
+          featuresExpected.setFeatures(pair._1());
+          featuresExpected.setExpected(pair._2());
+          return featuresExpected;
+        }
+      }
+    );
+
+    DataFrame df = sqlContext.createDataFrame(featuresExpected, VectorPair.class);
+    PCAModel pca = new PCA()
+      .setInputCol("features")
+      .setOutputCol("pca_features")
+      .setK(3)
+      .fit(df);
+    List<Row> result = pca.transform(df).select("pca_features", "expected").toJavaRDD().collect();
+    for (Row r : result) {
+      Assert.assertEquals(r.get(1), r.get(0));
+    }
+  }
+}