Java Collection Max partitionFixed(int maxNumChunks, Collection coll)

Description

Fills up chunks out of a collection (given a maximum amount of chunks) i.e.

License

Apache License

Parameter

Parameter	Description
maxNumChunks	the maximum number of chunks to return
coll	the collection to be chunked up

Return

a list of the chunks, which are themselves lists.

Declaration

public static <T> List<List<T>> partitionFixed(int maxNumChunks, Collection<T> coll) 

Method Source Code

//package com.java2s;
/*//from w ww  . j  a v a  2  s .c  o m
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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
 *
 * 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.Collection;
import java.util.Collections;

import java.util.Iterator;
import java.util.List;
import java.util.Map;

import java.util.TreeMap;

public class Main {
    /**
     * Fills up chunks out of a collection (given a maximum amount of chunks)
     *
     * i.e. partitionFixed(5, [1,2,3]) -> [[1,2,3]]
     *      partitionFixed(5, [1..9]) -> [[1,2], [3,4], [5,6], [7,8], [9]]
     *      partitionFixed(3, [1..10]) -> [[1,2,3,4], [5,6,7], [8,9,10]]
     * @param maxNumChunks the maximum number of chunks to return
     * @param coll the collection to be chunked up
     * @return a list of the chunks, which are themselves lists.
     */
    public static <T> List<List<T>> partitionFixed(int maxNumChunks, Collection<T> coll) {
        List<List<T>> ret = new ArrayList<>();

        if (maxNumChunks == 0 || coll == null) {
            return ret;
        }

        Map<Integer, Integer> parts = integerDivided(coll.size(), maxNumChunks);

        // Keys sorted in descending order
        List<Integer> sortedKeys = new ArrayList<Integer>(parts.keySet());
        Collections.sort(sortedKeys, Collections.reverseOrder());

        Iterator<T> it = coll.iterator();
        for (Integer chunkSize : sortedKeys) {
            if (!it.hasNext()) {
                break;
            }
            Integer times = parts.get(chunkSize);
            for (int i = 0; i < times; i++) {
                if (!it.hasNext()) {
                    break;
                }
                List<T> chunkList = new ArrayList<>();
                for (int j = 0; j < chunkSize; j++) {
                    if (!it.hasNext()) {
                        break;
                    }
                    chunkList.add(it.next());
                }
                ret.add(chunkList);
            }
        }

        return ret;
    }

    public static TreeMap<Integer, Integer> integerDivided(int sum, int numPieces) {
        int base = sum / numPieces;
        int numInc = sum % numPieces;
        int numBases = numPieces - numInc;
        TreeMap<Integer, Integer> ret = new TreeMap<Integer, Integer>();
        ret.put(base, numBases);
        if (numInc != 0) {
            ret.put(base + 1, numInc);
        }
        return ret;
    }

    public static <S, T> T get(Map<S, T> m, S key, T def) {
        T ret = m.get(key);
        if (ret == null) {
            ret = def;
        }
        return ret;
    }
}

Related

1. max(final Collection values)
2. max(final Collection collection)
3. maxLength(Collection strings)
4. maxOr(Collection values, T defaultVal)
5. minOrMax(int sign, Collection values)
6. toString(Collection collection, int maxLen)
7. toString(Collection entries, int max)
8. transfer(Collection source, Collection dest, int maxElems)
9. truncate(Collection coll, int maximumSize)