/**
* 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.mahout.common.iterator;
import java.util.Iterator;
import java.util.List;
import java.util.Random;
import com.google.common.collect.ForwardingIterator;
import com.google.common.collect.Lists;
import org.apache.mahout.common.RandomUtils;
/**
* Sample a fixed number of elements from an Iterator. The results can appear in any order.
*/
public final class FixedSizeSamplingIterator<T> extends ForwardingIterator<T> {
private final Iterator<T> delegate;
public FixedSizeSamplingIterator(int size, Iterator<T> source) {
List<T> buf = Lists.newArrayListWithCapacity(size);
int sofar = 0;
Random random = RandomUtils.getRandom();
while (source.hasNext()) {
T v = source.next();
sofar++;
if (buf.size() < size) {
buf.add(v);
} else {
int position = random.nextInt(sofar);
if (position < buf.size()) {
buf.set(position, v);
}
}
}
delegate = buf.iterator();
}
@Override
protected Iterator<T> delegate() {
return delegate;
}
}