Add test for Word2Vec algorithm, minor fixes

Author: Liquan Pei

mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala

@@ -50,24 +50,27 @@ private case class VocabWord(
  * natural language processing and machine learning algorithms.
  * 
  * We used skip-gram model in our implementation and hierarchical softmax 
- * method to train the model. 
+ * method to train the model. The variable names in the implementation
+ * mathes the original C implementation.
  *
  * For original C implementation, see https://code.google.com/p/word2vec/ 
  * For research papers, see 
  * Efficient Estimation of Word Representations in Vector Space
  * and 
- * Distributed Representations of Words and Phrases and their Compositionality
+ * Distributed Representations of Words and Phrases and their Compositionality.
  * @param size vector dimension
  * @param startingAlpha initial learning rate
  * @param window context words from [-window, window]
  * @param minCount minimum frequncy to consider a vocabulary word
+ * @param parallelisum number of partitions to run Word2Vec
  */
 @Experimental
 class Word2Vec(
     val size: Int,
     val startingAlpha: Double,
     val window: Int,
-    val minCount: Int) 
+    val minCount: Int,
+    val parallelism:Int = 1) 
   extends Serializable with Logging {
 
   private val EXP_TABLE_SIZE = 1000
@@ -237,7 +240,7 @@ class Word2Vec(
       }
     }
 
-    val newSentences = sentences.repartition(1).cache()
+    val newSentences = sentences.repartition(parallelism).cache()
     val temp = Array.fill[Double](vocabSize * layer1Size)((Random.nextDouble - 0.5) / layer1Size)
     val (aggSyn0, _, _, _) =
       // TODO: broadcast temp instead of serializing it directly 
@@ -248,7 +251,7 @@ class Word2Vec(
           var wc = wordCount 
           if (wordCount - lastWordCount > 10000) {
             lwc = wordCount
-            alpha = startingAlpha * (1 - wordCount.toDouble / (trainWordsCount + 1))
+            alpha = startingAlpha * (1 - parallelism * wordCount.toDouble / (trainWordsCount + 1))
             if (alpha < startingAlpha * 0.0001) alpha = startingAlpha * 0.0001
             logInfo("wordCount = " + wordCount + ", alpha = " + alpha)
           }
@@ -296,7 +299,7 @@ class Word2Vec(
             val n = syn0_1.length
             blas.daxpy(n, 1.0, syn0_2, 1, syn0_1, 1)
             blas.daxpy(n, 1.0, syn1_2, 1, syn1_1, 1)
-            (syn0_1, syn0_2, lwc_1 + lwc_2, wc_1 + wc_2)
+            (syn0_1, syn1_1, lwc_1 + lwc_2, wc_1 + wc_2)
         })
 
     val wordMap = new Array[(String, Array[Double])](vocabSize)
@@ -309,7 +312,7 @@ class Word2Vec(
       i += 1
     }
     val modelRDD = sc.parallelize(wordMap, modelPartitionNum)
-      .partitionBy(new HashPartitioner(modelPartitionNum))
+      .partitionBy(new HashPartitioner(modelPartitionNum)).cache()
     new Word2VecModel(modelRDD)
   }
 }

mllib/src/test/scala/org/apache/spark/mllib/feature/Word2VecSuite.scala

@@ -23,7 +23,27 @@ import org.apache.spark.SparkContext._
 import org.apache.spark.mllib.util.LocalSparkContext
 
 class Word2VecSuite extends FunSuite with LocalSparkContext {
-  test("word2vec") {
+  test("Word2Vec") {
+    val sentence = "a b " * 100 + "a c " * 10
+    val localDoc = Seq(sentence, sentence)
+    val doc = sc.parallelize(localDoc)
+      .map(line => line.split(" ").toSeq)
+    val size = 10
+    val startingAlpha = 0.025
+    val window = 2 
+    val minCount = 2
+    val num = 2
+    val word = "a"
+
+    val model = Word2Vec.train(doc, size, startingAlpha, window, minCount)
+    val synons = model.findSynonyms("a", 2)
+    assert(synons.length == num)
+    assert(synons(0)._1 == "b")
+    assert(synons(1)._1 == "c")
+  }
+
+
+  test("Word2VecModel") {
     val num = 2
     val localModel = Seq(
       ("china" ,  Array(0.50, 0.50, 0.50, 0.50)),