Java 8 流映射到按值排序的键列表
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Java 8 stream map to list of keys sorted by values
提问by adaPlease
I have map Map<Type, Long> countByTypeand I want to have a list which has sorted (min to max) keys by their corresponding values. My try is:
我有地图Map<Type, Long> countByType，我想要一个列表，该列表已按相应的值对（最小到最大）键进行排序。我的尝试是：
countByType.entrySet().stream().sorted().collect(Collectors.toList());
however this just gives me a list of entries, how can I get a list of types, without losing the order?
然而，这只是给了我一个条目列表，我怎样才能在不丢失订单的情况下获得类型列表？
采纳答案by Jesper
You say you want to sort by value, but you don't have that in your code. Pass a lambda (or method reference) to sortedto tell it how you want to sort.
你说你想按值排序，但你的代码中没有。传递一个 lambda（或方法引用）sorted来告诉它你想如何排序。
And you want to get the keys; use mapto transform entries to keys.
而你想拿到钥匙；用于map将条目转换为键。
List<Type> types = countByType.entrySet().stream()
.sorted(Comparator.comparing(Map.Entry::getValue))
.map(Map.Entry::getKey)
.collect(Collectors.toList());
回答by Sotirios Delimanolis
You have to sort with a custom comparator based on the value of the entry. Then select all the keys before collecting
您必须根据条目的值使用自定义比较器进行排序。然后在收集之前选择所有密钥
countByType.entrySet()
.stream()
.sorted((e1, e2) -> e1.getValue().compareTo(e2.getValue())) // custom Comparator
.map(e -> e.getKey())
.collect(Collectors.toList());
回答by Ajay Kumar
You can sort a map by value as below, more example here
您可以按值对地图进行排序，如下所示，更多示例在这里
//Sort a Map by their Value.
Map<Integer, String> random = new HashMap<Integer, String>();
random.put(1,"z");
random.put(6,"k");
random.put(5,"a");
random.put(3,"f");
random.put(9,"c");
Map<Integer, String> sortedMap =
random.entrySet().stream()
.sorted(Map.Entry.comparingByValue())
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
(e1, e2) -> e2, LinkedHashMap::new));
System.out.println("Sorted Map: " + Arrays.toString(sortedMap.entrySet().toArray()));
回答by user_3380739
回答by Kannan Msk
Map<Integer, String> map = new HashMap<>();
map.put(1, "B");
map.put(2, "C");
map.put(3, "D");
map.put(4, "A");
List<String> list = map.values().stream()
.sorted()
.collect(Collectors.toList());
Output: [A, B, C, D]
输出： [A, B, C, D]
回答by MADHUR GUPTA
You can use this as an example of your problem
你可以用这个作为你的问题的例子
Map<Integer, String> map = new HashMap<>();
map.put(10, "apple");
map.put(20, "orange");
map.put(30, "banana");
map.put(40, "watermelon");
map.put(50, "dragonfruit");
// split a map into 2 List
List<Integer> resultSortedKey = new ArrayList<>();
List<String> resultValues = map.entrySet().stream()
//sort a Map by key and stored in resultSortedKey
.sorted(Map.Entry.<Integer, String>comparingByKey().reversed())
.peek(e -> resultSortedKey.add(e.getKey()))
.map(x -> x.getValue())
// filter banana and return it to resultValues
.filter(x -> !"banana".equalsIgnoreCase(x))
.collect(Collectors.toList());
resultSortedKey.forEach(System.out::println);
resultValues.forEach(System.out::println);
