Java 8 Stream sort map of string to list based on list

Question

I have a map with key as string and value as list of strings

I want to sort the map based on the list of strings(Lexicographically).

If I have a List<List<String>> then I can sort by

List<List<String>> sortedlist = new LinkedList<>();
sortedlist.sort((l1, l2) -> l1.get(0).compareTo(l2.get(0)));

But I have a Map<String, List<String>> sortedMap and I want to sort this based on the values, i.e. first element of each list within the value set of the map.

I am trying to form a stream lambda expression something like this.

HashMap<String, List<String> > sortedmap = new HashMap<>();
sortedmap = map.values().stream().sorted(Map.Entry.comparingByValue((l1, l2) -> l1.get(0).compareTo(l2.get(0))) )

But it is not a valid lambda expression.

How do I do this with Java 8 streams?

ETO · Accepted Answer · 2019-10-09T14:31:05.563

2

Try this:

Map<String, List<String>> sortedMap = 
    map.entrySet() 
       .stream()
       .sorted(Map.Entry.comparingByValue(Comparator.comparing(l -> l.get(0))))
       .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (v1, v2) -> v1, LinkedHashMap::new));

Note that sorting would not make any sense while collecting into a HashMap, since it's unordered.

edited Oct 09 '19 at 14:31

answered Oct 09 '19 at 14:23

ETO

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This works. Thanks. Now trying to collect and print straightaway using foreach – Deepak Selvakumar Oct 09 '19 at 14:29
@DeepakSelvakumar Glad it helped. – ETO Oct 09 '19 at 14:32

Java 8 Stream sort map of string to list based on list

1 Answers1