edu.isi.nlp.collections.BootstrapIterator Maven / Gradle / Ivy
package edu.isi.nlp.collections;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.collect.AbstractIterator;
import com.google.common.collect.ImmutableCollection;
import com.google.common.collect.ImmutableList;
import java.util.Collection;
import java.util.Random;
/**
* An unbounded {@link java.util.Iterator} which provides a stream of bootstrap samples from a
* provided collection of items. If the "base" collection is of size N, this iterator will yield
* lists of size N where each element is sampled with replacement from the base collection.
*
* See https://en.wikipedia.org/wiki/Bootstrapping_%28statistics%29
*
*
{@author Ryan Gabbard}
*/
public final class BootstrapIterator extends AbstractIterator> {
private final Random rng;
private final ImmutableList data;
private BootstrapIterator(Iterable data, Random rng) {
this.data = ImmutableList.copyOf(data);
this.rng = checkNotNull(rng);
}
/**
* Creates a {@code BootstrapIterator} which samples from the provided {@code data}. This method
* takes in a {@code Random} to ensure determinism.
*/
public static BootstrapIterator forData(
Iterable data, Random rng) {
return new BootstrapIterator(data, rng);
}
@Override
protected ImmutableCollection computeNext() {
final ImmutableList.Builder ret = ImmutableList.builder();
if (data.isEmpty()) {
return ImmutableList.of();
}
for (int i = 0; i < data.size(); ++i) {
ret.add(data.get(rng.nextInt(data.size())));
}
return ret.build();
}
}