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?
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
在Java 8及以上版本中对任何地图进行排序的简单方法
Map<String, Object> mapToSort = new HashMap<>();
List<Map.Entry<String, Object>> list = new LinkedList<>(mapToSort.entrySet());
Collections.sort(list, Comparator.comparing(o -> o.getValue().getAttribute()));
HashMap<String, Object> sortedMap = new LinkedHashMap<>();
for (Map.Entry<String, Object> map : list) {
sortedMap.put(map.getKey(), map.getValue());
}
如果您使用的是Java 7及以下版本
Map<String, Object> mapToSort = new HashMap<>();
List<Map.Entry<String, Object>> list = new LinkedList<>(mapToSort.entrySet());
Collections.sort(list, new Comparator<Map.Entry<String, Object>>() {
@Override
public int compare(Map.Entry<String, Object> o1, Map.Entry<String, Object> o2) {
return o1.getValue().getAttribute().compareTo(o2.getValue().getAttribute());
}
});
HashMap<String, Object> sortedMap = new LinkedHashMap<>();
for (Map.Entry<String, Object> map : list) {
sortedMap.put(map.getKey(), map.getValue());
}
其他回答
我合并了user157196和Carter Page的解决方案:
class MapUtil {
public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue( Map<K, V> map ){
ValueComparator<K,V> bvc = new ValueComparator<K,V>(map);
TreeMap<K,V> sorted_map = new TreeMap<K,V>(bvc);
sorted_map.putAll(map);
return sorted_map;
}
}
class ValueComparator<K, V extends Comparable<? super V>> implements Comparator<K> {
Map<K, V> base;
public ValueComparator(Map<K, V> base) {
this.base = base;
}
public int compare(K a, K b) {
int result = (base.get(a).compareTo(base.get(b)));
if (result == 0) result=1;
// returning 0 would merge keys
return result;
}
}
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
}
public class SortedMapExample {
public static void main(String[] args) {
Map<String, String> map = new HashMap<String, String>();
map.put("Cde", "C");
map.put("Abc", "A");
map.put("Cbc", "Z");
map.put("Dbc", "D");
map.put("Bcd", "B");
map.put("sfd", "Bqw");
map.put("DDD", "Bas");
map.put("BGG", "Basd");
System.out.println(sort(map, new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
return o1.compareTo(o2);
}}));
}
@SuppressWarnings("unchecked")
public static <K, V> Map<K,V> sort(Map<K, V> in, Comparator<? super V> compare) {
Map<K, V> result = new LinkedHashMap<K, V>();
V[] array = (V[])in.values().toArray();
for(int i=0;i<array.length;i++)
{
}
Arrays.sort(array, compare);
for (V item : array) {
K key= (K) getKey(in, item);
result.put(key, item);
}
return result;
}
public static <K, V> Object getKey(Map<K, V> in,V value)
{
Set<K> key= in.keySet();
Iterator<K> keyIterator=key.iterator();
while (keyIterator.hasNext()) {
K valueObject = (K) keyIterator.next();
if(in.get(valueObject).equals(value))
{
return valueObject;
}
}
return null;
}
}
//请在这里尝试。我正在修改值排序的代码。
我们只需像这样对地图进行排序
Map<String, String> unsortedMap = new HashMap<String, String>();
unsortedMap.put("E", "E Val");
unsortedMap.put("F", "F Val");
unsortedMap.put("H", "H Val");
unsortedMap.put("B", "B Val");
unsortedMap.put("C", "C Val");
unsortedMap.put("A", "A Val");
unsortedMap.put("G", "G Val");
unsortedMap.put("D", "D Val");
Map<String, String> sortedMap = new TreeMap<String, String>(unsortedMap);
System.out.println("\nAfter sorting..");
for (Map.Entry <String, String> mapEntry : sortedMap.entrySet()) {
System.out.println(mapEntry.getKey() + " \t" + mapEntry.getValue());
最干净的方法是利用集合对值进行排序:
Map<String, Long> map = new HashMap<String, Long>();
// populate with data to sort on Value
// use datastructure designed for sorting
Queue queue = new PriorityQueue( map.size(), new MapComparable() );
queue.addAll( map.entrySet() );
// get a sorted map
LinkedHashMap<String, Long> linkedMap = new LinkedHashMap<String, Long>();
for (Map.Entry<String, Long> entry; (entry = queue.poll())!=null;) {
linkedMap.put(entry.getKey(), entry.getValue());
}
public static class MapComparable implements Comparator<Map.Entry<String, Long>>{
public int compare(Entry<String, Long> e1, Entry<String, Long> e2) {
return e1.getValue().compareTo(e2.getValue());
}
}