[GitHub] spark pull request: [ML][FEATURE] SPARK-5566: RegEx Tokenizer

[mengxr <gi...@git.apache.org>]

Github user mengxr commented on a diff in the pull request:

    https://github.com/apache/spark/pull/4504#discussion_r25232679
  
    --- Diff: mllib/src/main/scala/org/apache/spark/ml/feature/Tokenizer.scala ---
    @@ -39,3 +39,66 @@ class Tokenizer extends UnaryTransformer[String, Seq[String], Tokenizer] {
     
       override protected def outputDataType: DataType = new ArrayType(StringType, false)
     }
    +
    +
    +/**
    + * :: AlphaComponent ::
    + * A regex based tokenizer that extracts tokens using a regex.
    + * Optional additional parameters include enabling lowercase stabdarization, a minimum character
    + * size for tokens as well as an array of stop words to remove from the results.
    + */
    +@AlphaComponent
    +class RegexTokenizer extends UnaryTransformer[String, Seq[String], RegexTokenizer] {
    +
    +  val lowerCase = new BooleanParam(this, 
    +      "lowerCase", 
    +      "enable case folding to lower case", 
    +      Some(true))
    +  def setLowercase(value: Boolean) = set(lowerCase, value)
    +  def getLowercase: Boolean = get(lowerCase)
    +
    +  val minLength = new IntParam(this, 
    --- End diff --
    
    Add doc and update code style. What's the case when we match a token with regex but its length is zero? Should we control it in the regex, e.g., `\d{5,}`?
    
    Btw, it is not intuitive that the min value is excluded. Could we remove "excluded" and set the default value to `1`? And it might be better to call it `minTokenLength`, if we want to keep it.


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