CODEWITHSUNDEEP
android
Frink
Frink

Reputation: 221

Sorting array list method is to slow

First to say that I see very similar questions but i think this is not duplicate.

I need to sort string array list where members of list are in format ID::NAME and where ID is some number and name some string.

First idea was simple I use 

ArrayList<String> my_list = new ArrayList<String>();
my_list.add("0" + "::" + "ABC");
my_list.add("2" + "::" + "DBC");
my_list.add("1" + "::" + "DDC");
my_list.add("10" + "::" + "DBD");
my_list.add("22" + "::" + "DDD");
(etc...)
Collections.sort(my_list);

Problem is that in this method of sort "10" + "::" + "DBD" are before "1" + "::" + "DDC" etc I get something like:

0::ABC, 10::DBD, 1::DDC, 22::DDD, 2::DBC

And what i need is :

0::ABC, 1::DDC, 2::DBC, 10::DBD, 22::DDD

After this I try to make some temp integer list where i get all ID, sort this list , compare numbers with spliced value in my_list and get name from my list , to be clear this is code:

ArrayList<String> my_list = new ArrayList<String>();
ArrayList<String> sortedlist = new ArrayList<String>();
ArrayList<Integer> sortedTempIdlist = new ArrayList<Integer>();

my_list.add("0" + "::" + "ABC");
my_list.add("2" + "::" + "DBC");
my_list.add("1" + "::" + "DDC");
my_list.add("10" + "::" + "DBD");
my_list.add("22" + "::" + "DDD");
sortedTempIdlist(0);
sortedTempIdlist(2);
sortedTempIdlist(1);
sortedTempIdlist(10);
sortedTempIdlist(22);

Collections.sort(sortedTempIdlist);
for (int i = 0; i < sortedTempIdlist.size(); i++) {
    String temp = my_list.get(i);
    String[] s;

    try {
         s = temp.split("::");
         String name = s[1].toString();
         String id   = s[0].toString();

         for (String x : my_list) {
             Integer compare = Integer.valueOf(String.valueOf(x.split("::")[0]));
             if (sortedTempIdlist.get(i) == compare) { 
                  sortedlist.add(String.valueOf(sortedTempIdlist.get(i)) + "::" + String.valueOf(x.split("::")[1]));
             }
          }

    } catch (Exception e) {};
}

Now this work and sort list is ok but problem is that this work to slow when i have to many list member(lets say 600 or 1000). Is there faster way for something like this?

Thanx

Upvotes: 1

Views: 494

Answers (1)

Blackbelt
Blackbelt

Reputation: 157487

Wrap the id and the String in a small object:

public class Item {
   public int id;
   public String name;
}

and use Collections.sort() to sort the list agains the id:

Collections.sort(listInstance, new Comparator<Item>() {
     @Override
     public int compare(Item lhs, Item rhs) {
           return lhs.id < rhs.id ? - 1 : (lhs.id == rhs.id ? 0 : 1) ;
     }
 });

Collections.sort() will sort your list in O(nlogn)

Upvotes: 2

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