net.dontdrinkandroot.utils.collections.CollectionUtils.java Source code

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Here is the source code for net.dontdrinkandroot.utils.collections.CollectionUtils.java

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/**
 * Copyright (C) 2012 Philip W. Sorst <philip@sorst.net>
 * and individual contributors as indicated
 * by the @authors tag.
 *
 * 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 net.dontdrinkandroot.utils.collections;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedSet;
import java.util.TreeSet;

public class CollectionUtils extends org.apache.commons.collections15.CollectionUtils {

    public static <T extends Number> AggregationResult aggregate(final Collection<T> collection) {

        if (collection.isEmpty()) {
            throw new IllegalArgumentException("Collection must not be empty");
        }

        final AggregationResult result = new AggregationResult();
        result.setSize(collection.size());
        double sum = 0;
        double min = Double.MAX_VALUE;
        double max = Double.MIN_VALUE;

        /* Determine min, max, sum */
        for (final T entry : collection) {
            if (entry != null) {
                final double value = entry.doubleValue();
                max = Math.max(max, value);
                min = Math.min(min, value);
                sum += value;
            }
        }
        result.setMin(min);
        result.setMax(max);
        result.setSum(sum);

        result.setAvg(sum / result.getSize());

        result.setMean(CollectionUtils.getMean(collection));

        return result;
    }

    public static <T extends Number> double getMean(final Collection<T> collection) {

        final int size = collection.size();

        final List<T> sorted = new ArrayList<T>(collection);
        Collections.sort(sorted, new Comparator<T>() {

            @Override
            public int compare(final T n1, final T n2) {

                return (int) Math.signum(n2.doubleValue() - n1.doubleValue());
            }
        });

        if (size % 2 == 0) {
            return (sorted.get(size / 2).doubleValue() + sorted.get(size / 2 - 1).doubleValue()) / 2;
        } else {
            return sorted.get(size / 2).doubleValue();
        }
    }

    public static <T> T first(Iterable<T> iterable) {

        return iterable.iterator().next();
    }

    /**
     * Nullsafe check if a collection is empty.
     * 
     * @param obj
     *            Null or a subclass of Collection.
     * @throws IllegalArgumentException
     *             Thrown if obj is not null and not an instance of Collection.
     */
    public static boolean isEmpty(Object obj) {

        if (obj == null) {
            return true;
        }

        if (obj instanceof Collection) {
            return ((Collection<?>) obj).isEmpty();
        }

        throw new IllegalArgumentException("Given Object was not a collection");
    }

    public static <K, V> void addToMapList(K key, V value, Map<K, List<V>> map) {

        List<V> list = map.get(key);
        if (list == null) {
            list = new ArrayList<V>();
            map.put(key, list);
        }
        list.add(value);
    }

    public static <K, V> void addToMapSet(K key, V value, Map<K, Set<V>> map) {

        Set<V> set = map.get(key);
        if (set == null) {
            set = new HashSet<V>();
            map.put(key, set);
        }
        set.add(value);
    }

    public static <V> V getRandom(Collection<V> collection) {

        if (collection.isEmpty()) {
            return null;
        }

        int randIdx = (int) Math.round(Math.random() * (collection.size() - 1));
        int count = 0;
        Iterator<V> iterator = collection.iterator();
        while (iterator.hasNext()) {
            V current = iterator.next();
            if (count == randIdx) {
                return current;
            }
            count++;
        }

        throw new RuntimeException("Shouldn't happen");
    }

    public static <K, V extends Comparable<? super V>> SortedSet<Map.Entry<K, V>> entriesSortedByValues(
            Map<K, V> map) {

        SortedSet<Map.Entry<K, V>> sortedEntries = new TreeSet<Map.Entry<K, V>>(new Comparator<Map.Entry<K, V>>() {

            @Override
            public int compare(Map.Entry<K, V> e1, Map.Entry<K, V> e2) {

                int res = e1.getValue().compareTo(e2.getValue());
                /* Preserve items with equal values */
                return res != 0 ? res : 1;
            }
        });
        sortedEntries.addAll(map.entrySet());

        return sortedEntries;
    }

    public static <K, V extends Comparable<? super V>> SortedSet<Map.Entry<K, V>> entriesSortedByValuesInverse(
            Map<K, V> map) {

        SortedSet<Map.Entry<K, V>> sortedEntries = new TreeSet<Map.Entry<K, V>>(new Comparator<Map.Entry<K, V>>() {

            @Override
            public int compare(Map.Entry<K, V> e1, Map.Entry<K, V> e2) {

                int res = e2.getValue().compareTo(e1.getValue());
                /* Preserve items with equal values */
                return res != 0 ? res : -1;
            }
        });
        sortedEntries.addAll(map.entrySet());

        return sortedEntries;
    }

}