[SPARK-7583] [MLLIB] User guide update for RegexTokenizer

jira: https://issues.apache.org/jira/browse/SPARK-7583

User guide update for RegexTokenizer

Author: Yuhao Yang <hhbyyh@gmail.com>

Closes #7828 from hhbyyh/regexTokenizerDoc.

docs/ml-features.md

@@ -217,21 +217,32 @@ for feature in result.select("result").take(3):
 
 [Tokenization](http://en.wikipedia.org/wiki/Lexical_analysis#Tokenization) is the process of taking text (such as a sentence) and breaking it into individual terms (usually words).  A simple [Tokenizer](api/scala/index.html#org.apache.spark.ml.feature.Tokenizer) class provides this functionality.  The example below shows how to split sentences into sequences of words.
 
-Note: A more advanced tokenizer is provided via [RegexTokenizer](api/scala/index.html#org.apache.spark.ml.feature.RegexTokenizer).
+[RegexTokenizer](api/scala/index.html#org.apache.spark.ml.feature.RegexTokenizer) allows more
+ advanced tokenization based on regular expression (regex) matching.
+ By default, the parameter "pattern" (regex, default: \\s+) is used as delimiters to split the input text.
+ Alternatively, users can set parameter "gaps" to false indicating the regex "pattern" denotes
+ "tokens" rather than splitting gaps, and find all matching occurrences as the tokenization result.
 
 <div class="codetabs">
 <div data-lang="scala" markdown="1">
 {% highlight scala %}
-import org.apache.spark.ml.feature.Tokenizer
+import org.apache.spark.ml.feature.{Tokenizer, RegexTokenizer}
 
 val sentenceDataFrame = sqlContext.createDataFrame(Seq(
   (0, "Hi I heard about Spark"),
-  (0, "I wish Java could use case classes"),
-  (1, "Logistic regression models are neat")
+  (1, "I wish Java could use case classes"),
+  (2, "Logistic,regression,models,are,neat")
 )).toDF("label", "sentence")
 val tokenizer = new Tokenizer().setInputCol("sentence").setOutputCol("words")
-val wordsDataFrame = tokenizer.transform(sentenceDataFrame)
-wordsDataFrame.select("words", "label").take(3).foreach(println)
+val regexTokenizer = new RegexTokenizer()
+  .setInputCol("sentence")
+  .setOutputCol("words")
+  .setPattern("\\W")  // alternatively .setPattern("\\w+").setGaps(false)
+
+val tokenized = tokenizer.transform(sentenceDataFrame)
+tokenized.select("words", "label").take(3).foreach(println)
+val regexTokenized = regexTokenizer.transform(sentenceDataFrame)
+regexTokenized.select("words", "label").take(3).foreach(println)
 {% endhighlight %}
 </div>
 
@@ -240,6 +251,7 @@ wordsDataFrame.select("words", "label").take(3).foreach(println)
 import com.google.common.collect.Lists;
 
 import org.apache.spark.api.java.JavaRDD;
+import org.apache.spark.ml.feature.RegexTokenizer;
 import org.apache.spark.ml.feature.Tokenizer;
 import org.apache.spark.mllib.linalg.Vector;
 import org.apache.spark.sql.DataFrame;
@@ -252,8 +264,8 @@ import org.apache.spark.sql.types.StructType;
 
 JavaRDD<Row> jrdd = jsc.parallelize(Lists.newArrayList(
   RowFactory.create(0, "Hi I heard about Spark"),
-  RowFactory.create(0, "I wish Java could use case classes"),
-  RowFactory.create(1, "Logistic regression models are neat")
+  RowFactory.create(1, "I wish Java could use case classes"),
+  RowFactory.create(2, "Logistic,regression,models,are,neat")
 ));
 StructType schema = new StructType(new StructField[]{
   new StructField("label", DataTypes.DoubleType, false, Metadata.empty()),
@@ -267,22 +279,29 @@ for (Row r : wordsDataFrame.select("words", "label").take(3)) {
   for (String word : words) System.out.print(word + " ");
   System.out.println();
 }
+
+RegexTokenizer regexTokenizer = new RegexTokenizer()
+  .setInputCol("sentence")
+  .setOutputCol("words")
+  .setPattern("\\W");  // alternatively .setPattern("\\w+").setGaps(false);
 {% endhighlight %}
 </div>
 
 <div data-lang="python" markdown="1">
 {% highlight python %}
-from pyspark.ml.feature import Tokenizer
+from pyspark.ml.feature import Tokenizer, RegexTokenizer
 
 sentenceDataFrame = sqlContext.createDataFrame([
   (0, "Hi I heard about Spark"),
-  (0, "I wish Java could use case classes"),
-  (1, "Logistic regression models are neat")
+  (1, "I wish Java could use case classes"),
+  (2, "Logistic,regression,models,are,neat")
 ], ["label", "sentence"])
 tokenizer = Tokenizer(inputCol="sentence", outputCol="words")
 wordsDataFrame = tokenizer.transform(sentenceDataFrame)
 for words_label in wordsDataFrame.select("words", "label").take(3):
   print(words_label)
+regexTokenizer = RegexTokenizer(inputCol="sentence", outputCol="words", pattern="\\W")
+# alternatively, pattern="\\w+", gaps(False)
 {% endhighlight %}
 </div>
 </div>