Java Collection Count count(Collection collection)

License

Parameter

Return

Declaration

public static <A> Map<A, Integer> count(Collection<A> collection) 

Method Source Code

//package com.java2s;
/*******************************************************************************
 * Copyright (c) 2016 Pablo Pavon-Marino.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the GNU Lesser Public License v2.1
 * which accompanies this distribution, and is available at
 * http://www.gnu.org/licenses/lgpl.html
 *
 * Contributors:/*from  w  ww  . j av a2  s  .  co  m*/
 *     Pablo Pavon-Marino - Jose-Luis Izquierdo-Zaragoza, up to version 0.3.1
 *     Pablo Pavon-Marino - from version 0.4.0 onwards
 ******************************************************************************/

import java.util.*;

public class Main {
    /**
     * Returns a map where each entry represents the number of times that the
     * corresponding key appears in the input collection.
     *
     * @param <A> Key type
     * @param collection Input collection
     * @return Map where the key is an item appearing in the input collection, and the value is the number of times that appears
     */
    public static <A> Map<A, Integer> count(Collection<A> collection) {
        Map<A, Integer> out = new LinkedHashMap<A, Integer>();
        for (A value : collection)
            out.put(value, out.containsKey(value) ? out.get(value) + 1 : 1);

        return out;
    }
}

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