Github user dorx commented on a diff in the pull request: https://github.com/apache/spark/pull/1520#discussion_r15265778 --- Diff: mllib/src/main/scala/org/apache/spark/mllib/rdd/RandomRDD.scala --- @@ -0,0 +1,140 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.spark.mllib.rdd + +import org.apache.spark.{Partition, SparkContext, TaskContext} +import org.apache.spark.mllib.linalg.{DenseVector, Vector} +import org.apache.spark.mllib.random.DistributionGenerator +import org.apache.spark.rdd.RDD +import org.apache.spark.util.Utils + +private[mllib] class RandomRDDPartition(val idx: Int, + val size: Long, + val rng: DistributionGenerator, + val seed: Long) extends Partition { + + override val index: Int = idx + +} + +// These two classes are necessary since Range objects in Scala cannot have size > Int.MaxValue +private[mllib] class RandomRDD(@transient private var sc: SparkContext, + size: Long, + numSlices: Int, + @transient rng: DistributionGenerator, + @transient seed: Long = Utils.random.nextLong) extends RDD[Double](sc, Nil) { + + require(size > 0, "Positive RDD size required.") + require(numSlices > 0, "Positive number of partitions required") + + override def compute(splitIn: Partition, context: TaskContext): Iterator[Double] = { + val split = splitIn.asInstanceOf[RandomRDDPartition] + RandomRDD.getPointIterator(split) + } + + override def getPartitions: Array[Partition] = { + RandomRDD.getPartitions(size, numSlices, rng, seed) + } +} + +private[mllib] class RandomVectorRDD(@transient private var sc: SparkContext, + size: Long, + vectorSize: Int, + numSlices: Int, + @transient rng: DistributionGenerator, + @transient seed: Long = Utils.random.nextLong) extends RDD[Vector](sc, Nil) { + + require(size > 0, "Positive RDD size required.") + require(numSlices > 0, "Positive number of partitions required") + require(vectorSize > 0, "Positive vector size required.") + + override def compute(splitIn: Partition, context: TaskContext): Iterator[Vector] = { + val split = splitIn.asInstanceOf[RandomRDDPartition] + RandomRDD.getVectorIterator(split, vectorSize) + } + + override protected def getPartitions: Array[Partition] = { + RandomRDD.getPartitions(size, numSlices, rng, seed) + } +} + +private[mllib] object RandomRDD { + + private[mllib] class FixedSizePointIterator(val numElem: Long, val rng: DistributionGenerator) + extends Iterator[Double] { + + private var currentSize = 0 + + override def hasNext: Boolean = currentSize < numElem + + override def next(): Double = { + currentSize += 1 + rng.nextValue() + } + } + + private[mllib] class FixedSizeVectorIterator(val numElem: Long, + val vectorSize: Int, + val rng: DistributionGenerator) + extends Iterator[Vector] { + + private var currentSize = 0 + + override def hasNext: Boolean = currentSize < numElem + + override def next(): Vector = { + currentSize += 1 + new DenseVector((0 until vectorSize).map { _ => rng.nextValue() }.toArray) + } + } + + def getPartitions(size: Long, + numSlices: Int, + rng: DistributionGenerator, + seed: Long): Array[Partition] = { + + val firstPartitionSize = size / numSlices + size % numSlices + val otherPartitionSize = size / numSlices + + val partitions = new Array[RandomRDDPartition](numSlices) + var i = 0 + while (i < numSlices) { + partitions(i) = if (i == 0) { + new RandomRDDPartition(i, firstPartitionSize, rng, seed) + } else { + new RandomRDDPartition(i, otherPartitionSize, rng.newInstance(), seed) + } + i += 1 + } + partitions.asInstanceOf[Array[Partition]] + } + + // The RNG has to be reset every time the iterator is requested to guarantee same data + // every time the content of the RDD is examined. + def getPointIterator(partition: RandomRDDPartition): Iterator[Double] = { + partition.rng.setSeed(partition.seed + partition.index) --- End diff -- Thanks for the pointer to PartitionwiseSampledRDD. I've actually looked a lot at it for the sampling PRs. There were two considerations for going with this more deterministic seed assignment per partition. One is that this is a lot easier to test to make sure that each partition has a different seed with this deterministic seed assignment, and the other is that we're guaranteed to have a unique seed per partition. Since most RNG implementations hash or otherwise scramble the bits in the input seed before setting it anyway, I think we can get away with the current implementation.
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