[SPARK-11069][ML] Add RegexTokenizer option to convert to lowercase

jira: https://issues.apache.org/jira/browse/SPARK-11069
quotes from jira:
Tokenizer converts strings to lowercase automatically, but RegexTokenizer does not. It would be nice to add an option to RegexTokenizer to convert to lowercase. Proposal:
call the Boolean Param "toLowercase"
set default to false (so behavior does not change)

Actually sklearn converts to lowercase before tokenizing too

Author: Yuhao Yang <hhbyyh@gmail.com>

Closes #9092 from hhbyyh/tokenLower.

mllib/src/main/scala/org/apache/spark/ml/feature/Tokenizer.scala

@@ -100,10 +100,25 @@ class RegexTokenizer(override val uid: String)
   /** @group getParam */
   def getPattern: String = $(pattern)
 
-  setDefault(minTokenLength -> 1, gaps -> true, pattern -> "\\s+")
+  /**
+   * Indicates whether to convert all characters to lowercase before tokenizing.
+   * Default: true
+   * @group param
+   */
+  final val toLowercase: BooleanParam = new BooleanParam(this, "toLowercase",
+    "whether to convert all characters to lowercase before tokenizing.")
+
+  /** @group setParam */
+  def setToLowercase(value: Boolean): this.type = set(toLowercase, value)
+
+  /** @group getParam */
+  def getToLowercase: Boolean = $(toLowercase)
+
+  setDefault(minTokenLength -> 1, gaps -> true, pattern -> "\\s+", toLowercase -> true)
 
-  override protected def createTransformFunc: String => Seq[String] = { str =>
+  override protected def createTransformFunc: String => Seq[String] = { originStr =>
     val re = $(pattern).r
+    val str = if ($(toLowercase)) originStr.toLowerCase() else originStr
     val tokens = if ($(gaps)) re.split(str).toSeq else re.findAllIn(str).toSeq
     val minLength = $(minTokenLength)
     tokens.filter(_.length >= minLength)

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

@@ -53,6 +53,7 @@ public class JavaTokenizerSuite {
       .setOutputCol("tokens")
       .setPattern("\\s")
       .setGaps(true)
+      .setToLowercase(false)
       .setMinTokenLength(3);
 
 

mllib/src/test/scala/org/apache/spark/ml/feature/TokenizerSuite.scala

@@ -48,13 +48,13 @@ class RegexTokenizerSuite extends SparkFunSuite with MLlibTestSparkContext {
       .setInputCol("rawText")
       .setOutputCol("tokens")
     val dataset0 = sqlContext.createDataFrame(Seq(
-      TokenizerTestData("Test for tokenization.", Array("Test", "for", "tokenization", ".")),
-      TokenizerTestData("Te,st. punct", Array("Te", ",", "st", ".", "punct"))
+      TokenizerTestData("Test for tokenization.", Array("test", "for", "tokenization", ".")),
+      TokenizerTestData("Te,st. punct", Array("te", ",", "st", ".", "punct"))
     ))
     testRegexTokenizer(tokenizer0, dataset0)
 
     val dataset1 = sqlContext.createDataFrame(Seq(
-      TokenizerTestData("Test for tokenization.", Array("Test", "for", "tokenization")),
+      TokenizerTestData("Test for tokenization.", Array("test", "for", "tokenization")),
       TokenizerTestData("Te,st. punct", Array("punct"))
     ))
     tokenizer0.setMinTokenLength(3)
@@ -64,11 +64,23 @@ class RegexTokenizerSuite extends SparkFunSuite with MLlibTestSparkContext {
       .setInputCol("rawText")
       .setOutputCol("tokens")
     val dataset2 = sqlContext.createDataFrame(Seq(
-      TokenizerTestData("Test for tokenization.", Array("Test", "for", "tokenization.")),
-      TokenizerTestData("Te,st.  punct", Array("Te,st.", "punct"))
+      TokenizerTestData("Test for tokenization.", Array("test", "for", "tokenization.")),
+      TokenizerTestData("Te,st.  punct", Array("te,st.", "punct"))
     ))
     testRegexTokenizer(tokenizer2, dataset2)
   }
+
+  test("RegexTokenizer with toLowercase false") {
+    val tokenizer = new RegexTokenizer()
+      .setInputCol("rawText")
+      .setOutputCol("tokens")
+      .setToLowercase(false)
+    val dataset = sqlContext.createDataFrame(Seq(
+      TokenizerTestData("JAVA SCALA", Array("JAVA", "SCALA")),
+      TokenizerTestData("java scala", Array("java", "scala"))
+    ))
+    testRegexTokenizer(tokenizer, dataset)
+  }
 }
 
 object RegexTokenizerSuite extends SparkFunSuite {