Java 使用 lambdas 和流按值对地图进行排序
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Sort map by value using lambdas and streams
提问by Sudarsana Kasireddy
I'm new to Java 8, not sure how to use streams and it's methods to sort. If I have map as below, how to sort this map by value to take only top 10 entries using Java 8.
我是 Java 8 的新手，不确定如何使用流及其排序方法。如果我有如下地图，如何使用 Java 8 按值对该地图进行排序以仅获取前 10 个条目。
HashMap<String, Integer> map = new HashMap<String, Integer>();
map.put("a", 10);
map.put("b", 30);
map.put("c", 50);
map.put("d", 40);
map.put("e", 100);
map.put("f", 60);
map.put("g", 110);
map.put("h", 50);
map.put("i", 90);
map.put("k", 70);
map.put("L", 80);
I know before Java 8, we can sort as this link: https://stackoverflow.com/a/109389/4315608
我知道在 Java 8 之前，我们可以按这个链接排序：https: //stackoverflow.com/a/109389/4315608
采纳答案by ericbn
You can always start reading the documentationand sometutorials.
map.entrySet().stream()
.sorted(Map.Entry.<String, Integer>comparingByValue().reversed())
.limit(10)
.forEach(System.out::println); // or any other terminal method
Reference
参考
http://www.leveluplunch.com/java/examples/sort-order-map-by-values/
http://www.leveluplunch.com/java/examples/sort-order-map-by-values/
回答by pomo
List<Map.Entry<String, Integer>> entries = newArrayList(map.entrySet());
Collections.sort(entries, (o1, o2) -> o1.getValue().compareTo(o2.getValue()));
List<Map.Entry<String, Integer>> top10 = entries.subList(0, Math.min(entries.size(), 10));
回答by Ajay Kumar
See the stack flow thread hereand example here
Map<String,Person> map = new HashMap<>();
map.put("g",new Person(5, "EE", 51, Person.SEX.FEMALE, "A"));
map.put("a",new Person(4, "DD", 25, Person.SEX.MALE, "D"));
map.put("e",new Person(3, "CC", 44, Person.SEX.FEMALE,"B"));
Map<String,Person> sortedNewMap = map.entrySet().stream().sorted((e1,e2)->
e1.getValue().getLocation().compareTo(e2.getValue().getLocation()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
(e1, e2) -> e1, LinkedHashMap::new));
sortedNewMap.forEach((key,val)->{
System.out.println(key+ " = "+ val.toString());
});
回答by Nycrera
If you want sort by integer or float value of value object
如果要按值对象的整数或浮点值排序
Map<String,Person> map = new HashMap<>();
map.put("g",new Person(5, "EE", 51, Person.SEX.FEMALE, "A"));
map.put("a",new Person(4, "DD", 25, Person.SEX.MALE, "D"));
map.put("e",new Person(3, "CC", 44, Person.SEX.FEMALE,"B"));
You can use,
您可以使用，
Map<String,Person> sortedNewMap = map.entrySet().stream().sorted((e1,e2)->
Integer.compare(e1.getValue().getAge(), e2.getValue().getAge()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
(e1, e2) -> e1, LinkedHashMap::new));
