Java 8 how to sort list of list of map

Question

I have code like this

List<List<Map<String, String>>> outerList = new ArrayList<>();
List<Map<String, String>> innerList = new ArrayList<>();
outerList.add(innerList)

How to sort outerList using java8 based on the map values. I do not want the inner list to be sorted.

Example:

List<Map<String, String>> innerList1 = new ArrayList<>(); 
Map<String, String> map1= new HashMap<String, String>();
map1.put("sort", "2")
innerList1.add(map1);

List<Map<String, String>> innerList2 = new ArrayList<>(); 
Map<String, String> map2 = new HashMap<String, String>();
map2.put("sort", "1")
innerList2.add(map2);

outerList.add(innerList1);
outerList.add(innerList2);

after sorting the innerList2 should be first in the list and innerlist1 should be second Since the sort value is 2 and 1;

Implement a comparator which will let you compare 2 elements of your list and then sort the list using the comparator. Have a look here https://stackoverflow.com/questions/2784514/sort-arraylist-of-custom-objects-by-property — Olivier Depriester, Sep 22 '20 at 07:00
Please provide an example how do you expect to sort _outer_ list by the map values which are unsorted. — Nowhere Man, Sep 22 '20 at 07:02
What are your constraints on sorting? E.g. how would you like to sort the outer list based on the inner map? — Lino, Sep 22 '20 at 07:19

Rahul Jain · Answer 1 · 2020-09-22T09:53:03.893

0

Assuming sorting based on 1st element of outerList and "sort" key of map

below lambda expression will work for you.

List<List<Map<String, String>>> collect = outerList.stream().sorted((e1, e2) -> e1.get(0).get("sort").compareTo(e2.get(0).get("sort"))).collect(Collectors.toList());

Without Streams:

outerList.sort((e1, e2) -> e1.get(0).get("sort").compareTo(e2.get(0).get("sort")));

With comparator:

outerList.sort(new Comparator<List<Map<String,String>>>() {
        @Override
        public int compare(List<Map<String, String>> e1, List<Map<String, String>> e2) {

        <your logic here>
            return <int value>;
        });

edited Sep 22 '20 at 09:53

answered Sep 22 '20 at 09:15

Rahul Jain

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Thanks for the answer ! But the sort map will not be first element or the only element. The inner list has many for other maps added to it. sorry for not being clear. – Sharath N B Sep 22 '20 at 09:45
you can edit the logic you want in the sort method `sort((e1, e2) -> );` – Rahul Jain Sep 22 '20 at 09:50
Thanks! I am trying this. – Sharath N B Sep 22 '20 at 10:49

Java 8 how to sort list of list of map

1 Answers1