CODEWITHSUNDEEP
javasortingarraylistjava-6
Mr.Chowdary
Mr.Chowdary

Reputation: 3407

sort list of list based on size of the subList?

I have a List of List. I want to sort the Super List depends on the sub list size. The Lists are dynamic.
The List type is <ArrayList<ArrayList<HashMap>>> Eg.

[ [{key1=value1,key2=value2}],[],[{key1=value1}],[{key1=value1},{key2=value2},{key3=value3}]  ]

After The sorting it should display 

[[{key1=value1},{key2=value2},{key3=value3}], [{key1=value1,key2=value2}],[{key1=value1}],[]  ]

Can you help how to sort this?

Thanks in advance.
Laxman chowdary

Upvotes: 3

Views: 2962

Answers (4)

alain.janinm
alain.janinm

Reputation: 20065

EDITED :

If you want to sort a List of List of Map ordered by List of Map size you can do this.

Note that you can change the order of parameters (o1 and o2) in Integer.valueOf(o1.size()).compareTo(o2.size()) to sort in the decreasing order.

public static <T> List<? extends List<T>> sortListByValue(List<? extends List<T>> list) {

    Collections.sort(list, new Comparator<List<T>>() {


        @Override
        public int compare(List<T> o1, List<T> o2) {
            //return Integer.compare(o1.size(), o2.size()); //JDK7 

            //Use this if you're using a version prior to 1.7.
            return Integer.valueOf(o1.size()).compareTo(o2.size());
        }
    });

    return list;
}   


public static void main(String[] args) {

    ArrayList<Map<String,String>> list1 = new ArrayList<>();
    list1.add(new HashMap<String, String>(){{ put("1", "a"); put("2", "b");}});
    list1.add(new HashMap<String, String>(){{ put("1", "a"); put("2", "b"); put("3", "c");}});
    list1.add(new HashMap<String, String>(){{ put("1", "a"); }});

    ArrayList<Map<String,String>> list2 = new ArrayList<>();
    list2.add(new HashMap<String, String>(){{ put("1", "a"); put("2", "b");}});
    list2.add(new HashMap<String, String>(){{ put("1", "a"); put("2", "b"); put("3", "c");}});

    ArrayList<Map<String,String>> list3 = new ArrayList<>();
    list3.add(new HashMap<String, String>(){{ put("1", "a"); put("2", "b");}});

    ArrayList<ArrayList<Map<String,String>>> list = new ArrayList<>();
    list.add(list1);
    list.add(list2);
    list.add(list3);
    System.out.println(list);
    System.out.println(sortListByValue(list));
}

Upvotes: 6

Fabian Barney
Fabian Barney

Reputation: 14549

public static <T> List<List<T>> sortBySublistSize(List<List<T>> superList) {
    Collections.sort(superList, new Comparator<List<T>>() {
        @Override
        public int compare(List<T> o1, List<T> o2) {
            return Integer.compare(o1.size(), o2.size());
        }
    });

    return superList;
}

Upvotes: 1

Wojciech Owczarczyk
Wojciech Owczarczyk

Reputation: 5735

Collections.sort(list, new Comparator<List<? extends Map>>() {
        public int compare(List<? extends Map> list1, List<? extends Map> list2) {
            return Integer.valueOf(list1.size()).compareTo(Integer.valueOf(list2.size()));
        }
    });

If you do not take care about generics that much you can simplify it such as:

Collections.sort(list, new Comparator<List>() {
            public int compare(List list1, List list2) {
                return Integer.valueOf(list1.size()).compareTo(Integer.valueOf(list2.size()));
            }
        });

Upvotes: 2

Jon Taylor
Jon Taylor

Reputation: 7905

You can use any normal sort algorithm but instead of basing on value just base on the length of the element instead.

Upvotes: 0

Related Questions