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From zsxwing <...@git.apache.org>
Subject [GitHub] spark pull request: [SPARK-7150] add range() api
Date Thu, 14 May 2015 15:54:03 GMT
Github user zsxwing commented on a diff in the pull request:

    https://github.com/apache/spark/pull/6081#discussion_r30332931
  
    --- Diff: core/src/main/scala/org/apache/spark/SparkContext.scala ---
    @@ -689,6 +689,58 @@ class SparkContext(config: SparkConf) extends Logging with ExecutorAllocationCli
         new ParallelCollectionRDD[T](this, seq, numSlices, Map[Int, Seq[String]]())
       }
     
    +  /**
    +   * Creates a new RDD[Long] containing elements from `start` to `end`(exclusive), increased
by
    +   * `step` every element.
    +   *
    +   * @note if we need to cache this RDD, we should make sure each partition does not
exceed limit.
    +   *
    +   * @param start the start value.
    +   * @param end the end value.
    +   * @param step the incremental step
    +   * @param numSlices the partition number of the new RDD.
    +   * @return
    +   */
    +  def range(
    +      start: Long,
    +      end: Long,
    +      step: Long = 1,
    +      numSlices: Int = defaultParallelism): RDD[Long] = withScope {
    +    assertNotStopped()
    +    // when step is 0, range will run infinitely
    +    require(step != 0, "step cannot be 0")
    +    val numElements: BigInt = {
    +      val safeStart = BigInt(start)
    +      val safeEnd = BigInt(end)
    +      if (((safeEnd - safeStart) % step).toInt == 0) {
    +        (safeEnd - safeStart) / step
    +      } else {
    +        (safeEnd - safeStart) / step + 1
    +      }
    +    }
    +    parallelize(0 until numSlices, numSlices).mapPartitionsWithIndex((i, _) => {
    +      val partitionStart = ((i * numElements) / numSlices * step + start).toLong
    +      val partitionEnd = (((i + 1) * numElements) / numSlices * step + start).toLong
    --- End diff --
    
    As our previous discussion, `partitionEnd` may exceed `end`. If `end` is `Long.MaxValue`,
`partitionEnd` may overflow. Could you compare it with `Long.MaxValue` before converting it
to `Long`, and set it to `Long.MaxValue` if `partitionEnd` overflow?


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