[SPARK-7586] [ML] [DOC] Add docs of Word2Vec in ml package

CC jkbradley.

JIRA [issue](https://issues.apache.org/jira/browse/SPARK-7586).

Author: Xusen Yin <yinxusen@gmail.com>

Closes #6181 from yinxusen/SPARK-7586 and squashes the following commits:

77014c5 [Xusen Yin] comment fix
57a4c07 [Xusen Yin] small fix for docs
1178c8f [Xusen Yin] remove the correctness check in java suite
1c3f389 [Xusen Yin] delete sbt commit
1af152b [Xusen Yin] check python example code
1b5369e [Xusen Yin] add docs of word2vec

docs/ml-features.md

@@ -106,6 +106,95 @@ for features_label in featurized.select("features", "label").take(3):
 </div>
 </div>
 
+## Word2Vec
+
+`Word2Vec` is an `Estimator` which takes sequences of words that represents documents and trains a `Word2VecModel`. The model is a `Map(String, Vector)` essentially, which maps each word to an unique fix-sized vector. The `Word2VecModel` transforms each documents into a vector using the average of all words in the document, which aims to other computations of documents such as similarity calculation consequencely. Please refer to the [MLlib user guide on Word2Vec](mllib-feature-extraction.html#Word2Vec) for more details on Word2Vec.
+
+Word2Vec is implemented in [Word2Vec](api/scala/index.html#org.apache.spark.ml.feature.Word2Vec). In the following code segment, we start with a set of documents, each of them is represented as a sequence of words. For each document, we transform it into a feature vector. This feature vector could then be passed to a learning algorithm.
+
+<div class="codetabs">
+<div data-lang="scala" markdown="1">
+{% highlight scala %}
+import org.apache.spark.ml.feature.Word2Vec
+
+// Input data: Each row is a bag of words from a sentence or document.
+val documentDF = sqlContext.createDataFrame(Seq(
+  "Hi I heard about Spark".split(" "),
+  "I wish Java could use case classes".split(" "),
+  "Logistic regression models are neat".split(" ")
+).map(Tuple1.apply)).toDF("text")
+
+// Learn a mapping from words to Vectors.
+val word2Vec = new Word2Vec()
+  .setInputCol("text")
+  .setOutputCol("result")
+  .setVectorSize(3)
+  .setMinCount(0)
+val model = word2Vec.fit(documentDF)
+val result = model.transform(documentDF)
+result.select("result").take(3).foreach(println)
+{% endhighlight %}
+</div>
+
+<div data-lang="java" markdown="1">
+{% highlight java %}
+import com.google.common.collect.Lists;
+
+import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.sql.DataFrame;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.RowFactory;
+import org.apache.spark.sql.SQLContext;
+import org.apache.spark.sql.types.*;
+
+JavaSparkContext jsc = ...
+SQLContext sqlContext = ...
+
+// Input data: Each row is a bag of words from a sentence or document.
+JavaRDD<Row> jrdd = jsc.parallelize(Lists.newArrayList(
+  RowFactory.create(Lists.newArrayList("Hi I heard about Spark".split(" "))),
+  RowFactory.create(Lists.newArrayList("I wish Java could use case classes".split(" "))),
+  RowFactory.create(Lists.newArrayList("Logistic regression models are neat".split(" ")))
+));
+StructType schema = new StructType(new StructField[]{
+  new StructField("text", new ArrayType(DataTypes.StringType, true), false, Metadata.empty())
+});
+DataFrame documentDF = sqlContext.createDataFrame(jrdd, schema);
+
+// Learn a mapping from words to Vectors.
+Word2Vec word2Vec = new Word2Vec()
+  .setInputCol("text")
+  .setOutputCol("result")
+  .setVectorSize(3)
+  .setMinCount(0);
+Word2VecModel model = word2Vec.fit(documentDF);
+DataFrame result = model.transform(documentDF);
+for (Row r: result.select("result").take(3)) {
+  System.out.println(r);
+}
+{% endhighlight %}
+</div>
+
+<div data-lang="python" markdown="1">
+{% highlight python %}
+from pyspark.ml.feature import Word2Vec
+
+# Input data: Each row is a bag of words from a sentence or document.
+documentDF = sqlContext.createDataFrame([
+  ("Hi I heard about Spark".split(" "), ),
+  ("I wish Java could use case classes".split(" "), ),
+  ("Logistic regression models are neat".split(" "), )
+], ["text"])
+# Learn a mapping from words to Vectors.
+word2Vec = Word2Vec(vectorSize=3, minCount=0, inputCol="text", outputCol="result")
+model = word2Vec.fit(documentDF)
+result = model.transform(documentDF)
+for feature in result.select("result").take(3):
+  print(feature)
+{% endhighlight %}
+</div>
+</div>
 
 # Feature Transformers
 

mllib/src/test/java/org/apache/spark/ml/feature/JavaWord2VecSuite.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 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.JavaRDD;
+import org.apache.spark.api.java.JavaSparkContext;
+import org.apache.spark.mllib.linalg.Vector;
+import org.apache.spark.sql.DataFrame;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.RowFactory;
+import org.apache.spark.sql.SQLContext;
+import org.apache.spark.sql.types.*;
+
+public class JavaWord2VecSuite {
+  private transient JavaSparkContext jsc;
+  private transient SQLContext sqlContext;
+
+  @Before
+  public void setUp() {
+    jsc = new JavaSparkContext("local", "JavaWord2VecSuite");
+    sqlContext = new SQLContext(jsc);
+  }
+
+  @After
+  public void tearDown() {
+    jsc.stop();
+    jsc = null;
+  }
+
+  @Test
+  public void testJavaWord2Vec() {
+    JavaRDD<Row> jrdd = jsc.parallelize(Lists.newArrayList(
+      RowFactory.create(Lists.newArrayList("Hi I heard about Spark".split(" "))),
+      RowFactory.create(Lists.newArrayList("I wish Java could use case classes".split(" "))),
+      RowFactory.create(Lists.newArrayList("Logistic regression models are neat".split(" ")))
+    ));
+    StructType schema = new StructType(new StructField[]{
+      new StructField("text", new ArrayType(DataTypes.StringType, true), false, Metadata.empty())
+    });
+    DataFrame documentDF = sqlContext.createDataFrame(jrdd, schema);
+
+    Word2Vec word2Vec = new Word2Vec()
+      .setInputCol("text")
+      .setOutputCol("result")
+      .setVectorSize(3)
+      .setMinCount(0);
+    Word2VecModel model = word2Vec.fit(documentDF);
+    DataFrame result = model.transform(documentDF);
+
+    for (Row r: result.select("result").collect()) {
+      double[] polyFeatures = ((Vector)r.get(0)).toArray();
+      Assert.assertEquals(polyFeatures.length, 3);
+    }
+  }
+}