Java 8 stream map to list of keys sorted by values

Question

I have map Map lt Type  Long gt  countByType and I want to have a list which has sorted  min to max  keys by their corresponding values  My try is   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

User · Answer

Map lt Integer  String gt  map   new HashMap lt  gt     map put 1   quot B quot    map put 2   quot C quot    map put 3   quot D quot    map put 4   quot A quot     List lt String gt  list   map values                           stream                           sorted                           collect Collectors toList      Output   A  B  C  D

User · Answer

You can use this as an example of your problem      Map lt Integer  String gt  map   new HashMap lt  gt         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 lt Integer gt  resultSortedKey   new ArrayList lt  gt         List lt String gt  resultValues   map entrySet   stream                 sort a Map by key and stored in resultSortedKey              sorted Map Entry  lt Integer  String gt comparingByKey   reversed                 peek e - gt  resultSortedKey add e getKey                  map x - gt  x getValue                   filter banana and return it to resultValues              filter x - gt    banana  equalsIgnoreCase x                collect Collectors toList          resultSortedKey forEach System out  println       resultValues forEach System out  println

User · Answer

You have to sort with a custom comparator based on the value of the entry  Then select all the keys before collecting  countByType entrySet               stream               sorted  e1  e2  - gt  e1 getValue   compareTo e2 getValue        custom Comparator             map e - gt  e getKey                collect Collectors toList

User · Answer

Here is the simple solution with StreamEx  EntryStream of countByType  sortedBy e - gt  e getValue    keys   toList

User · Answer

You can sort a map by value as below  more example here    Sort a Map by their Value  Map lt Integer  String gt  random   new HashMap lt Integer  String gt      random put 1  z    random put 6  k    random put 5  a    random put 3  f    random put 9  c     Map lt Integer  String gt  sortedMap           random entrySet   stream                    sorted Map Entry comparingByValue                     collect Collectors toMap Map Entry  getKey  Map Entry  getValue                           e1  e2  - gt  e2  LinkedHashMap  new    System out println  Sorted Map      Arrays toString sortedMap entrySet   toArray

User · Answer

You say you want to sort by value  but you don t have that in your code  Pass a lambda  or method reference  to sorted to tell it how you want to sort   And you want to get the keys  use map to transform entries to keys   List lt Type gt  types   countByType entrySet   stream            sorted Comparator comparing Map Entry  getValue            map Map Entry  getKey           collect Collectors toList

[java] Java 8 stream map to list of keys sorted by values

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