CODEWITHSUNDEEP
javajava-8
Yakkanti
Yakkanti

Reputation: 63

How to sort keys in a map based on elements in a list

I would like arrange/sort elements in a map based the keys available in a list ( order of elements in a list is immutable) such that keys in map and list should be in same order using java.

Data in a map :

{grocery=150, utility=130, miscellneous=90, rent=1150,
 clothes=120, transportation=100}

Data in a list :

[utility, miscellneous, clothes, transportation, rent]

Expected Result :

{utility=130, miscellneous=90, clothes=120, transportation=100, rent=1150 }

Upvotes: 2

Views: 96

Answers (3)

davidxxx
davidxxx

Reputation: 131546

That is not a sort. You want to process the elements by starting from the list.
Supposing that the textual values be String and that the numeric values be Integer, you could do that : 

Map<String, Integer> finalMap = 
list.stream()
    .collect(toMap(o->o, map.get(o), (a,b)->a, LinkedHashMap::new));

or still : 

LinkedHashMap<String, Integer> finalMap = new LinkedHashMap<>();
list.forEach(o-> finalMap.put(o, map.get(o));

Upvotes: 3

Oleg Cherednik
Oleg Cherednik

Reputation: 18255

You have to iterate over the required list of keys and retrieve the values from the Map. To keep order, you should use LinkedHashMap:

public static Map<String, Integer> sort(Map<String, Integer> map, String[] keys) {
    return Arrays.stream(keys).collect(Collectors.toMap(key -> key, map::get, Integer::sum, LinkedHashMap::new));
}

Upvotes: 0

Amardeep Bhowmick
Amardeep Bhowmick

Reputation: 16908

You can sort the map based on the index of occurrence of the key of the map in the given list by using a Comparator then to preserve the sort order collect it to a LinkedHashMap :

public static void main(String[] args) throws Exception {
        Map<String, Integer> map = new HashMap<>();
        map.put("grocery", 150);
        map.put("utility", 130);
        map.put("miscellneous", 90);
        map.put("rent", 1150);
        map.put("clothes", 120);
        map.put("transportation", 100);

        List<String> list = new ArrayList<>(
                            Arrays.asList("utility", "miscellneous", "clothes", 
                                          "transportation", "rent"));
        Map<String, Integer> sortedMap 
        = map.keySet()
             .stream()
             .filter(list::contains)
             .sorted(Comparator.comparing(list::indexOf))
             .collect(LinkedHashMap::new, 
                     (linkMap, key) -> linkMap.put(key, map.get(key)), 
                     Map::putAll);

        System.out.println(sortedMap);
 }

Output:

 {utility=130, miscellneous=90, clothes=120, transportation=100, rent=1150}

Upvotes: 0

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