Sorts map by values in ascending order. : Map « Collections Data Structure « Java






  1. Java
  2. Collections Data Structure
  3. Map

Sorts map by values in ascending order.

      
//package sk.hasto.java.collections;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

/**
 * Utility functions for working with Maps.
 * 
 * @author Branislav Hasto
 */
public final class MapUtils {

  /**
   * Sorts map by values in ascending order.
   * 
   * @param <K>
   *            map keys type
   * @param <V>
   *            map values type
   * @param map
   * @return
   */
  public static <K, V extends Comparable<V>> LinkedHashMap<K, V> sortMapByValue(
      Map<K, V> map) {
    List<Entry<K, V>> sortedEntries = sortEntriesByValue(map.entrySet());
    LinkedHashMap<K, V> sortedMap = new LinkedHashMap<K, V>(map.size());
    for (Entry<K, V> entry : sortedEntries) {
      sortedMap.put(entry.getKey(), entry.getValue());
    }

    return sortedMap;
  }

  /**
   * Sorts map entries by value in ascending order.
   * 
   * @param <K>
   *            map keys type
   * @param <V>
   *            map values type
   * @param entries
   * @return
   */
  private static <K, V extends Comparable<V>> List<Entry<K, V>> sortEntriesByValue(
      Set<Entry<K, V>> entries) {
    List<Entry<K, V>> sortedEntries = new ArrayList<Entry<K, V>>(entries);
    Collections.sort(sortedEntries, new ValueComparator<V>());
    return sortedEntries;
  }

  /**
   * Komparator podla hodnot v polozkach mapy.
   * 
   * @param <V>
   *            typ hodnot
   */
  private static class ValueComparator<V extends Comparable<V>> implements
      Comparator<Entry<?, V>> {
    public int compare(Entry<?, V> entry1, Entry<?, V> entry2) {
      return entry1.getValue().compareTo(entry2.getValue());
    }
  }

}








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