Java Collection Count countDuplicates(Collection items)

Description

count Duplicates

License

Apache License

Declaration

static <T> List<Object> countDuplicates(Collection<T> items) 

Method Source Code

//package com.java2s;
/*/* www  .j ava2s.c o  m*/
 * Copyright (c) 2011 Google, Inc.
 *
 * 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.
 */

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;

import java.util.List;

public class Main {
    static <T> List<Object> countDuplicates(Collection<T> items) {
        // We use a List to de-dupe instead of a Set in case the elements don't have a proper
        // .hashCode() method (e.g., MessageSet from old versions of protobuf).
        List<T> itemSet = new ArrayList<T>();
        for (T item : items) {
            if (!itemSet.contains(item)) {
                itemSet.add(item);
            }
        }
        Object[] params = new Object[itemSet.size()];
        int n = 0;
        for (T item : itemSet) {
            int count = countOf(item, items);
            params[n++] = (count > 1) ? item + " [" + count + " copies]" : item;
        }
        return Arrays.asList(params);
    }

    static <T> int countOf(T t, Iterable<T> items) {
        int count = 0;
        for (T item : items) {
            if (t == null ? (item == null) : t.equals(item)) {
                count++;
            }
        }
        return count;
    }
}

Related

1. count(final Collection blocks)
2. count(T x0, T x1, T x2, Collection sentences)
3. count(V matching, Collection values)
4. countCollectionsSize(Collection... cols)
5. countComplement(Collection s1, Collection s2)
6. countOverlappers(Collection distances)