ai.djl.training.dataset.RandomSampler Maven / Gradle / Ivy
/*
* Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except in compliance
* with the License. A copy of the License is located at
*
* http://aws.amazon.com/apache2.0/
*
* or in the "license" file accompanying this file. This file 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 ai.djl.training.dataset;
import ai.djl.util.RandomUtils;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Random;
import java.util.stream.LongStream;
/**
* {@code RandomSampler} is an implementation of the {@link
* ai.djl.training.dataset.Sampler.SubSampler} interface.
*
* {@code RandomSampler} samples the data from [0, dataset.size) randomly.
*/
public class RandomSampler implements Sampler.SubSampler {
private Integer seed;
/** Creates a new instance of {@code RandomSampler}. */
public RandomSampler() {}
/**
* Creates a new instance of {@code RandomSampler} with the given seed.
*
* @param seed the value of the seed
*/
public RandomSampler(int seed) {
this.seed = seed;
}
private static void swap(long[] arr, int i, int j) {
long tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
/** {@inheritDoc} */
@Override
public Iterator sample(RandomAccessDataset dataset) {
return new Iterate(dataset, seed);
}
static class Iterate implements Iterator {
private long[] indices;
private long current;
Iterate(RandomAccessDataset dataset, Integer seed) {
long size = dataset.size();
current = 0;
indices = LongStream.range(0, size).toArray();
Random rnd = (seed != null) ? new Random(seed) : RandomUtils.RANDOM;
// java array didn't support index greater than max integer
// so cast to int for now
for (int i = Math.toIntExact(size) - 1; i > 0; --i) {
swap(indices, i, rnd.nextInt(i));
}
}
/** {@inheritDoc} */
@Override
public boolean hasNext() {
return current < indices.length;
}
/** {@inheritDoc} */
@Override
public Long next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
// java array didn't support index greater than max integer
// so cast to int for now
return indices[Math.toIntExact(current++)];
}
}
}