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Added validation check for parallelizing a seq #329

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Added validation check for parallelizing a seq #329

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22 changes: 13 additions & 9 deletions core/src/main/scala/org/apache/spark/rdd/ParallelCollectionRDD.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -112,6 +112,7 @@ private object ParallelCollectionRDD {
* it efficient to run Spark over RDDs representing large sets of numbers.
*/
def slice[T: ClassTag](seq: Seq[T], numSlices: Int): Seq[Seq[T]] = {
def validNumSlices(vSeq: Seq[_]) = if (vSeq.length < numSlices) vSeq.length else numSlices
if (numSlices < 1) {
throw new IllegalArgumentException("Positive number of slices required")
}
Expand All @@ -126,28 +127,31 @@ private object ParallelCollectionRDD {
r.start, r.end + sign, r.step).asInstanceOf[Seq[T]], numSlices)
}
case r: Range => {
(0 until numSlices).map(i => {
val start = ((i * r.length.toLong) / numSlices).toInt
val end = (((i + 1) * r.length.toLong) / numSlices).toInt
val vNumSlices = validNumSlices(r)
(0 until vNumSlices).map(i => {
val start = ((i * r.length.toLong) / vNumSlices).toInt
val end = (((i + 1) * r.length.toLong) / vNumSlices).toInt
new Range(r.start + start * r.step, r.start + end * r.step, r.step)
}).asInstanceOf[Seq[Seq[T]]]
}
case nr: NumericRange[_] => {
// For ranges of Long, Double, BigInteger, etc
val slices = new ArrayBuffer[Seq[T]](numSlices)
val sliceSize = (nr.size + numSlices - 1) / numSlices // Round up to catch everything
val vNumSlices = validNumSlices(nr)
val slices = new ArrayBuffer[Seq[T]](vNumSlices)
var r = nr
for (i <- 0 until numSlices) {
for (i <- 0 until vNumSlices) {
val sliceSize = (((i + 1) * nr.length.toLong) / vNumSlices).toInt - ((i * nr.length.toLong) / vNumSlices).toInt
slices += r.take(sliceSize).asInstanceOf[Seq[T]]
r = r.drop(sliceSize)
}
slices
}
case _ => {
val vNumSlices = validNumSlices(seq)
val array = seq.toArray // To prevent O(n^2) operations for List etc
(0 until numSlices).map(i => {
val start = ((i * array.length.toLong) / numSlices).toInt
val end = (((i + 1) * array.length.toLong) / numSlices).toInt
(0 until vNumSlices).map(i => {
val start = ((i * array.length.toLong) / vNumSlices).toInt
val end = (((i + 1) * array.length.toLong) / vNumSlices).toInt
array.slice(start, end).toSeq
})
}
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