我对Java比较陌生,经常发现需要对值进行Map<Key,Value>排序。

由于这些值不是唯一的,我发现自己将keySet转换为一个数组,并使用自定义比较器通过数组排序对该数组进行排序,该比较器根据与该键关联的值进行排序。

有没有更简单的方法?


当前回答

这种方法正好能达到目的。(“挫折”是Values必须实现java.util.Comparable接口)

  /**

 * Sort a map according to values.

 * @param <K> the key of the map.
 * @param <V> the value to sort according to.
 * @param mapToSort the map to sort.

 * @return a map sorted on the values.

 */ 
public static <K, V extends Comparable< ? super V>> Map<K, V>
sortMapByValues(final Map <K, V> mapToSort)
{
    List<Map.Entry<K, V>> entries =
        new ArrayList<Map.Entry<K, V>>(mapToSort.size());  

    entries.addAll(mapToSort.entrySet());

    Collections.sort(entries,
                     new Comparator<Map.Entry<K, V>>()
    {
        @Override
        public int compare(
               final Map.Entry<K, V> entry1,
               final Map.Entry<K, V> entry2)
        {
            return entry1.getValue().compareTo(entry2.getValue());
        }
    });      

    Map<K, V> sortedMap = new LinkedHashMap<K, V>();      

    for (Map.Entry<K, V> entry : entries)
    {
        sortedMap.put(entry.getKey(), entry.getValue());

    }      

    return sortedMap;

}

http://javawithswaranga.blogspot.com/2011/06/generic-method-to-sort-hashmap.html

其他回答

基于@devinmore代码,一种使用泛型并支持升序和降序排序的map排序方法。

/**
 * Sort a map by it's keys in ascending order. 
 *  
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByKey(final Map<K, V> map) {
    return sortMapByKey(map, SortingOrder.ASCENDING);
}

/**
 * Sort a map by it's values in ascending order.
 *  
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByValue(final Map<K, V> map) {
    return sortMapByValue(map, SortingOrder.ASCENDING);
}

/**
 * Sort a map by it's keys.
 *  
 * @param sortingOrder {@link SortingOrder} enum specifying requested sorting order. 
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByKey(final Map<K, V> map, final SortingOrder sortingOrder) {
    Comparator<Map.Entry<K, V>> comparator = new Comparator<Entry<K,V>>() {
        public int compare(Entry<K, V> o1, Entry<K, V> o2) {
            return comparableCompare(o1.getKey(), o2.getKey(), sortingOrder);
        }
    };

    return sortMap(map, comparator);
}

/**
 * Sort a map by it's values.
 *  
 * @param sortingOrder {@link SortingOrder} enum specifying requested sorting order. 
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMapByValue(final Map<K, V> map, final SortingOrder sortingOrder) {
    Comparator<Map.Entry<K, V>> comparator = new Comparator<Entry<K,V>>() {
        public int compare(Entry<K, V> o1, Entry<K, V> o2) {
            return comparableCompare(o1.getValue(), o2.getValue(), sortingOrder);
        }
    };

    return sortMap(map, comparator);
}

@SuppressWarnings("unchecked")
private static <T> int comparableCompare(T o1, T o2, SortingOrder sortingOrder) {
    int compare = ((Comparable<T>)o1).compareTo(o2);

    switch (sortingOrder) {
    case ASCENDING:
        return compare;
    case DESCENDING:
        return (-1) * compare;
    }

    return 0;
}

/**
 * Sort a map by supplied comparator logic.
 *  
 * @return new instance of {@link LinkedHashMap} contained sorted entries of supplied map.
 * @author Maxim Veksler
 */
public static <K, V> LinkedHashMap<K, V> sortMap(final Map<K, V> map, final Comparator<Map.Entry<K, V>> comparator) {
    // Convert the map into a list of key,value pairs.
    List<Map.Entry<K, V>> mapEntries = new LinkedList<Map.Entry<K, V>>(map.entrySet());

    // Sort the converted list according to supplied comparator.
    Collections.sort(mapEntries, comparator);

    // Build a new ordered map, containing the same entries as the old map.  
    LinkedHashMap<K, V> result = new LinkedHashMap<K, V>(map.size() + (map.size() / 20));
    for(Map.Entry<K, V> entry : mapEntries) {
        // We iterate on the mapEntries list which is sorted by the comparator putting new entries into 
        // the targeted result which is a sorted map. 
        result.put(entry.getKey(), entry.getValue());
    }

    return result;
}

/**
 * Sorting order enum, specifying request result sort behavior.
 * @author Maxim Veksler
 *
 */
public static enum SortingOrder {
    /**
     * Resulting sort will be from smaller to biggest.
     */
    ASCENDING,
    /**
     * Resulting sort will be from biggest to smallest.
     */
    DESCENDING
}

这太复杂了。地图不应该按价值排序。最简单的方法是创建自己的类,以满足您的需求。

在下面的示例中,您应该在*所在的位置添加TreeMap比较器。但通过javaAPI,它只提供比较器键,而不提供值。此处所述的所有示例均基于2个地图。一个哈希和一个新树。这很奇怪。

示例:

Map<Driver driver, Float time> map = new TreeMap<Driver driver, Float time>(*);

因此,通过以下方式将地图更改为集合:

ResultComparator rc = new ResultComparator();
Set<Results> set = new TreeSet<Results>(rc);

您将创建类Results,

public class Results {
    private Driver driver;
    private Float time;

    public Results(Driver driver, Float time) {
        this.driver = driver;
        this.time = time;
    }

    public Float getTime() {
        return time;
    }

    public void setTime(Float time) {
        this.time = time;
    }

    public Driver getDriver() {
        return driver;
    }

    public void setDriver (Driver driver) {
        this.driver = driver;
    }
}

以及Comparator类:

public class ResultsComparator implements Comparator<Results> {
    public int compare(Results t, Results t1) {
        if (t.getTime() < t1.getTime()) {
            return 1;
        } else if (t.getTime() == t1.getTime()) {
            return 0;
        } else {
            return -1;
        }
    }
}

这样,您可以轻松添加更多依赖项。

最后一点,我将添加简单迭代器:

Iterator it = set.iterator();
while (it.hasNext()) {
    Results r = (Results)it.next();
    System.out.println( r.getDriver().toString
        //or whatever that is related to Driver class -getName() getSurname()
        + " "
        + r.getTime()
        );
}

最好的方法是将HashMap转换为TreeMap。TreeMap自己排序键。如果您希望对值进行排序,则可以快速修复,如果您的值不重复,则可以使用键切换值。

如果没有大于地图大小的值,可以使用数组,这应该是最快的方法:

public List<String> getList(Map<String, Integer> myMap) {
    String[] copyArray = new String[myMap.size()];
    for (Entry<String, Integer> entry : myMap.entrySet()) {
        copyArray[entry.getValue()] = entry.getKey();
    }
    return Arrays.asList(copyArray);
}

使用LinkedList

//Create a list by HashMap
List<Map.Entry<String, Double>> list = new LinkedList<>(hashMap.entrySet());

//Sorting the list
Collections.sort(list, new Comparator<Map.Entry<String, Double>>() {
    public int compare(Map.Entry<String, Double> o1, Map.Entry<String, Double> o2) {
        return (o1.getValue()).compareTo(o2.getValue());
    }
});

//put data from sorted list to hashmap
HashMap<String, Double> sortedData = new LinkedHashMap<>();
for (Map.Entry<String, Double> data : list) {
    sortedData.put(data.getKey(), data.getValue());
}

System.out.print(sortedData);