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
Geeks For Geeks对HashMap按值排序
Input : Key = Math, Value = 98
Key = Data Structure, Value = 85
Key = Database, Value = 91
Key = Java, Value = 95
Key = Operating System, Value = 79
Key = Networking, Value = 80
Output : Key = Operating System, Value = 79
Key = Networking, Value = 80
Key = Data Structure, Value = 85
Key = Database, Value = 91
Key = Java, Value = 95
Key = Math, Value = 98
Solution: The idea is to store the entry set in a list and sort the list on the basis of values. Then fetch values and keys from the list and put them in a new hashmap. Thus, a new hashmap is sorted according to values.
Below is the implementation of the above idea:
// Java program to sort hashmap by values
import java.util.*;
import java.lang.*;
public class GFG {
// function to sort hashmap by values
public static HashMap<String, Integer> sortByValue(HashMap<String, Integer> hm)
{
// Create a list from elements of HashMap
List<Map.Entry<String, Integer> > list =
new LinkedList<Map.Entry<String, Integer> >(hm.entrySet());
// Sort the list
Collections.sort(list, new Comparator<Map.Entry<String, Integer> >() {
public int compare(Map.Entry<String, Integer> o1,
Map.Entry<String, Integer> o2)
{
return (o1.getValue()).compareTo(o2.getValue());
}
});
// put data from sorted list to hashmap
HashMap<String, Integer> temp = new LinkedHashMap<String, Integer>();
for (Map.Entry<String, Integer> aa : list) {
temp.put(aa.getKey(), aa.getValue());
}
return temp;
}
// Driver Code
public static void main(String[] args)
{
HashMap<String, Integer> hm = new HashMap<String, Integer>();
// enter data into hashmap
hm.put("Math", 98);
hm.put("Data Structure", 85);
hm.put("Database", 91);
hm.put("Java", 95);
hm.put("Operating System", 79);
hm.put("Networking", 80);
Map<String, Integer> hm1 = sortByValue(hm);
// print the sorted hashmap
for (Map.Entry<String, Integer> en : hm1.entrySet()) {
System.out.println("Key = " + en.getKey() +
", Value = " + en.getValue());
}
}
}
Output
Key = Operating System, Value = 79
Key = Networking, Value = 80
Key = Data Structure, Value = 85
Key = Database, Value = 91
Key = Java, Value = 95
Key = Math, Value = 98
其他回答
您可以尝试Guava的多功能地图:
TreeMap<Integer, Collection<String>> sortedMap = new TreeMap<>(
Multimaps.invertFrom(Multimaps.forMap(originalMap),
ArrayListMultimap.<Integer, String>create()).asMap());
因此,您将获得从原始值到对应于它们的键集合的映射。即使同一值有多个键,也可以使用此方法。
因为地图是无序的要对其进行排序,我们可以执行以下操作
Map<String, String> map= new TreeMap<String, String>(unsortMap);
您应该注意,与哈希映射不同,树映射保证其元素将按升序键排序。
使用Guava库:
public static <K,V extends Comparable<V>>SortedMap<K,V> sortByValue(Map<K,V> original){
var comparator = Ordering.natural()
.reverse() // highest first
.nullsLast()
.onResultOf(Functions.forMap(original, null))
.compound(Ordering.usingToString());
return ImmutableSortedMap.copyOf(original, comparator);
}
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()
);
}
map = your hashmap;
List<Map.Entry<String, Integer>> list = new LinkedList<Map.Entry<String, Integer>>(map.entrySet());
Collections.sort(list, new cm());//IMP
HashMap<String, Integer> sorted = new LinkedHashMap<String, Integer>();
for(Map.Entry<String, Integer> en: list){
sorted.put(en.getKey(),en.getValue());
}
System.out.println(sorted);//sorted hashmap
创建新类
class cm implements Comparator<Map.Entry<String, Integer>>{
@Override
public int compare(Map.Entry<String, Integer> a,
Map.Entry<String, Integer> b)
{
return (a.getValue()).compareTo(b.getValue());
}
}