1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package org.apache.commons.rng.sampling;
19
20 import java.util.Collection;
21 import java.util.List;
22 import java.util.ArrayList;
23
24 import org.apache.commons.rng.UniformRandomProvider;
25
26 /**
27 * Sampling from a {@link Collection}.
28 *
29 * @param <T> Type of items in the collection.
30 *
31 * @since 1.0
32 */
33 public class CollectionSampler<T> {
34 /** Collection to be sampled from. */
35 private final List<T> items;
36 /** RNG. */
37 private final UniformRandomProvider rng;
38
39 /**
40 * Creates a sampler.
41 *
42 * @param rng Generator of uniformly distributed random numbers.
43 * @param collection Collection to be sampled.
44 * A (shallow) copy will be stored in the created instance.
45 * @throws IllegalArgumentException if {@code collection} is empty.
46 */
47 public CollectionSampler(UniformRandomProvider rng,
48 Collection<T> collection) {
49 if (collection.isEmpty()) {
50 throw new IllegalArgumentException("Empty collection");
51 }
52
53 this.rng = rng;
54 items = new ArrayList<T>(collection);
55 }
56
57 /**
58 * Picks one of the items from the
59 * {@link #CollectionSampler(UniformRandomProvider,Collection)
60 * collection passed to the constructor}.
61 *
62 * @return a random sample.
63 */
64 public T sample() {
65 return items.get(rng.nextInt(items.size()));
66 }
67 }