com.cloudera.science.ml.core.vectors.Weighted.java Source code

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Here is the source code for com.cloudera.science.ml.core.vectors.Weighted.java

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/**
 * Copyright (c) 2012, Cloudera, Inc. All Rights Reserved.
 *
 * Cloudera, Inc. 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
 *
 * This software 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 com.cloudera.science.ml.core.vectors;

import java.util.Collection;
import java.util.List;
import java.util.Random;
import java.util.SortedMap;

import com.google.common.base.Function;
import com.google.common.base.Preconditions;
import com.google.common.collect.Collections2;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.primitives.Doubles;

/**
 * A typed container for an object and an associated numeric weight.
 */
public class Weighted<T> {
    private final T thing;
    private final double weight;

    private static class WeightFunction<T> implements Function<T, Weighted<T>> {
        @Override
        public Weighted<T> apply(T input) {
            return new Weighted<T>(input);
        }
    }

    /**
     * Converts an input {@code Collection<T>} into a {@code Collection<Weighted<T>>}.
     * 
     * @param things The items to convert
     * @return The items as {@code Weighted<T>} values with weight 1.0
     */
    public static <T> Collection<Weighted<T>> create(Collection<T> things) {
        return Collections2.transform(things, new WeightFunction<T>());
    }

    /**
     * Converts an input {@code List<T>} into a {@code List<Weighted<T>>}.
     * 
     * @param things The items to convert
     * @return The items as {@code Weighted<T>} values with weight 1.0
     */
    public static <T> List<Weighted<T>> create(List<T> things) {
        return Lists.transform(things, new WeightFunction<T>());
    }

    /**
     * Sample items from a {@code List<Weighted<T>>} where items with higher weights
     * have a higher probability of being included in the sample.
     * 
     * @param things The iterable to sample from
     * @param size The number of items to sample
     * @return A list containing the sampled items
     */
    public static <T> List<Weighted<T>> sample(Iterable<Weighted<T>> things, int size, Random random) {
        if (random == null) {
            random = new Random();
        }
        SortedMap<Double, Weighted<T>> sampled = Maps.newTreeMap();
        for (Weighted<T> thing : things) {
            if (thing.weight() > 0) {
                double score = Math.log(random.nextDouble()) / thing.weight();
                if (sampled.size() < size || score > sampled.firstKey()) {
                    sampled.put(score, thing);
                }
                if (sampled.size() > size) {
                    sampled.remove(sampled.firstKey());
                }
            }
        }
        return Lists.newArrayList(sampled.values());
    }

    /**
     * Create a new instance with weight 1.0.
     * 
     * @param thing The thing that is weighted
     */
    public Weighted(T thing) {
        this(thing, 1.0);
    }

    /**
     * Create a new instance with the given weight.
     * 
     * @param thing The (non-null) thing to weight
     * @param weight The weight
     */
    public Weighted(T thing, double weight) {
        this.thing = Preconditions.checkNotNull(thing);
        this.weight = weight;
    }

    /**
     * Return the thing referenced by this instance.
     */
    public T thing() {
        return thing;
    }

    /**
     * Return the numeric weight for this instance.
     */
    public double weight() {
        return weight;
    }

    @Override
    public boolean equals(Object other) {
        if (!(other instanceof Weighted)) {
            return false;
        }
        Weighted<T> wv = (Weighted<T>) other;
        return thing.equals(wv.thing) && weight == wv.weight;
    }

    @Override
    public int hashCode() {
        return 17 * thing.hashCode() + 37 * Doubles.hashCode(weight);
    }

    @Override
    public String toString() {
        return String.valueOf(thing) + ';' + weight;
    }
}