| /* |
| * 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.commons.rng.sampling; |
| |
| import java.util.Collection; |
| import java.util.List; |
| import java.util.ArrayList; |
| |
| import org.apache.commons.rng.UniformRandomProvider; |
| |
| /** |
| * Sampling from a {@link Collection}. |
| * |
| * @param <T> Type of items in the collection. |
| * |
| * @since 1.0 |
| */ |
| public class CollectionSampler<T> { |
| /** Collection to be sampled from. */ |
| private final List<T> items; |
| /** RNG. */ |
| private final UniformRandomProvider rng; |
| |
| /** |
| * Creates a sampler. |
| * |
| * @param rng Generator of uniformly distributed random numbers. |
| * @param collection Collection to be sampled. |
| * A (shallow) copy will be stored in the created instance. |
| * @throws IllegalArgumentException if {@code collection.size() <= 0}. |
| */ |
| public CollectionSampler(UniformRandomProvider rng, |
| Collection<T> collection) { |
| if (collection.size() <= 0) { |
| throw new IllegalArgumentException("Empty collection"); |
| } |
| |
| this.rng = rng; |
| items = new ArrayList<T>(collection); |
| } |
| |
| /** |
| * Picks one of the items in the given {@code collection}. |
| * |
| * <p> |
| * Sampling is without replacement; but if the source collection |
| * contains identical objects, the sample may include repeats. |
| * </p> |
| * <p> |
| * There is no guarantee that the concrete type of the returned |
| * collection is the same as the source collection. |
| * </p> |
| * |
| * @return a random sample. |
| */ |
| public T sample() { |
| return items.get(rng.nextInt(items.size())); |
| } |
| } |