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From ygcao <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-12153][SPARK-7617][MLlib]add support of...
Date Wed, 17 Feb 2016 05:38:14 GMT
Github user ygcao commented on a diff in the pull request:

    https://github.com/apache/spark/pull/10152#discussion_r53122840
  
    --- Diff: mllib/src/main/scala/org/apache/spark/mllib/feature/Word2Vec.scala ---
    @@ -289,24 +301,20 @@ class Word2Vec extends Serializable with Logging {
         val expTable = sc.broadcast(createExpTable())
         val bcVocab = sc.broadcast(vocab)
         val bcVocabHash = sc.broadcast(vocabHash)
    -
    -    val sentences: RDD[Array[Int]] = words.mapPartitions { iter =>
    -      new Iterator[Array[Int]] {
    -        def hasNext: Boolean = iter.hasNext
    -
    -        def next(): Array[Int] = {
    -          val sentence = ArrayBuilder.make[Int]
    -          var sentenceLength = 0
    -          while (iter.hasNext && sentenceLength < MAX_SENTENCE_LENGTH) {
    -            val word = bcVocabHash.value.get(iter.next())
    -            word match {
    -              case Some(w) =>
    -                sentence += w
    -                sentenceLength += 1
    -              case None =>
    -            }
    +    // each partition is a collection of sentences,
    +    // will be translated into arrays of Index integer
    +    val sentences: RDD[Array[Int]] = dataset.mapPartitions { sentenceIter =>
    +      // Each sentence will map to 0 or more Array[Int]
    +      sentenceIter.flatMap { sentence => {
    +          // Sentence of words, some of which map to a word index
    +          val wordIndexes = sentence.flatMap(bcVocabHash.value.get)
    +          if (wordIndexes.nonEmpty) {
    --- End diff --
    
    You guys are right. didn't quite get @mengxr 's previous explanation. The splitting function
is doing something unexpected to me, split an empty String will result in a non empty array.
    FYI. I verified the logic using following codes to be more explicit test, which proved
your assertions.
    scala> sentences
    res4: List[List[String]] = List(List(a, b, c), List(b), List(c, d))
    
    scala> dict
    res5: scala.collection.immutable.Map[String,Int] = Map(a -> 1, c -> 2)
    
    scala> sentences.flatMap(sen=>{val indexes=sen.flatMap(dict.get);indexes.grouped(2).map(_.toArray)})
    res6: List[Array[Int]] = List(Array(1, 2), Array(2))
    
    scala> "".split(" ")
    res7: Array[String] = Array("")
    
    scala> "".split(" ").size
    res8: Int = 1



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