com.insightml.math.distributions.DiscreteDistribution.java Source code

Introduction

Here is the source code for com.insightml.math.distributions.DiscreteDistribution.java

Source

/*
 * Copyright (C) 2016 Stefan Hen
 *
 * Licensed 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 com.insightml.math.distributions;

import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Random;

import org.apache.commons.math3.util.Pair;

import com.google.common.base.Preconditions;
import com.insightml.math.types.SumMap;
import com.insightml.math.types.SumMap.SumMapBuilder;
import com.insightml.utils.Check;
import com.insightml.utils.types.AbstractClass;

public final class DiscreteDistribution<T> extends AbstractClass
        implements IDiscreteDistribution<T>, Iterable<Entry<T, Double>> {

    private static final long serialVersionUID = -8857716547353316720L;

    private LinkedHashMap<T, Double> map;

    public DiscreteDistribution() {
    }

    DiscreteDistribution(final LinkedHashMap<T, Double> map) {
        this.map = map;
    }

    public boolean contains(final T key) {
        return map.containsKey(key);
    }

    @Override
    public double get(final T key) {
        return Check.notNull(map.get(key), key).doubleValue();
    }

    public double get(final T key, final double defaultValue) {
        final Double value = map.get(key);
        return value == null ? defaultValue : value.doubleValue();
    }

    @Override
    public Pair<T, Double> getMax() {
        double max = 0;
        T key = null;
        for (final Entry<T, Double> entry : map.entrySet()) {
            if (entry.getValue() > max) {
                max = entry.getValue();
                key = entry.getKey();
            }
        }
        return new Pair<>(key, max);
    }

    @Override
    public T sample(final Random random) {
        if (map.size() == 1) {
            return map.keySet().iterator().next();
        }
        final double rand = random.nextDouble();
        double sum = 0;
        for (final Entry<T, Double> entry : map.entrySet()) {
            sum += entry.getValue();
            if (rand <= sum) {
                return entry.getKey();
            }
        }
        throw new IllegalStateException();
    }

    public SumMap<T> filter(final double min) {
        final SumMapBuilder<T> builder = new SumMapBuilder<>(true, false);
        for (final Entry<T, Double> entry : map.entrySet()) {
            if (entry.getValue() >= min) {
                builder.put(entry.getKey(), entry.getValue());
            }
        }
        return builder.build(0);
    }

    public int size() {
        return map.size();
    }

    public boolean isEmpty() {
        return map.isEmpty();
    }

    public Map<T, Double> getMap() {
        return map;
    }

    @Override
    public Iterator<Entry<T, Double>> iterator() {
        return map.entrySet().iterator();
    }

    public static int sample(final double[] discreteDistribution, final Random random) {
        final double rand = random.nextDouble();
        double sum = 0;
        for (int i = 0; i < discreteDistribution.length; ++i) {
            sum += discreteDistribution[i];
            if (rand <= sum) {
                return i;
            }
        }
        throw new IllegalStateException(rand + " / " + sum);
    }

    @Override
    public String toString() {
        return map.toString();
    }

    public static final class DistributionBuilder<T> {
        private final Map<T, Double> map = new LinkedHashMap<>();

        public void put(final T key, final double value) {
            Check.state(
                    value >= -0.0001 && value <= 1.0001 && map.put(Preconditions.checkNotNull(key), value) == null);
        }

        public DiscreteDistribution<T> build() {
            validate();
            return new DiscreteDistribution<>(new LinkedHashMap<>(map));
        }

        private void validate() {
            if (map.isEmpty()) {
                return;
            }
            double sum = 0;
            for (final Double value : map.values()) {
                sum += value.doubleValue();
            }
            Check.num(sum, 0.9999999, 1.0000001);
        }
    }

}