CODEWITHSUNDEEP
javaarraylistdistinct
dcts
dcts

Reputation: 1639

Label distinct values for Arraylist<String> with identifier

I have a simple problem. I have an ArrayList (of type String) with 100'000 Names. I want to create another ArrayList (of type Integer) which also has 100'000 Elements and assignes each Element of the String ArrayList an ID-Number. Equal Names should have equal ID Numbers assigned.
VERY BASIC EXAMPLE:
i have: (hans, max, hans, hans, frank)
i want: ( 1 , 2 , 1 , 1 , 3 )

I implemented a Solution which works, but is very slow (for my big dataset of 100'000 Names). I wonder someone can find a better/faster way of doing this. Thanks everyone for any tipps! 

public static void main(String[] args) {        

    // initialize arraylists
    ArrayList<String>  Names      = new ArrayList<String>();
    ArrayList<Integer> Id         = new ArrayList<Integer>();   

    // sample data              // I want the integer Arraylist to have values:
    Names.add("Hans");          // 1 
    Names.add("Max");           // 2
    Names.add("Hans");          // 1
    Names.add("Hans");          // 1
    Names.add("Frank");         // 3

    // my solution (works, but is slow and confusing)
    int N = Names.size();
    int ID_Count = 0;
    for (int i=0; i<N; i++) {
        boolean match_found = false;
        String curr_Name = Names.get(i);
        for (int check=0; check<i; check++) {
            if (curr_Name.equals(Names.get(check))) {
                Id.add(Id.get(check));
                match_found = true;
                break;
            }
        }
        if (match_found==false) {
            ID_Count++;
            Id.add(ID_Count);
        }
    }

    // show result
    for (int i=0; i<N; i++) {
        System.out.println(Id.get(i) + " " + Names.get(i));
    }
}

Upvotes: 0

Views: 615

Answers (2)

Leonardo Cruz
Leonardo Cruz

Reputation: 1189

This is a faster way of doing it:

    public static void main(String[] args) {

    // initialize arraylists
    ArrayList<String> Names      = new ArrayList<String>();
    Map<String,Integer> map      = new HashMap<>();

    // sample data              // I want the integer Arraylist to have values:
    Names.add("Hans");          // 1
    Names.add("Max");           // 2
    Names.add("Hans");          // 1
    Names.add("Hans");          // 1
    Names.add("Frank");         // 3

    int N = Names.size();

    int id = 0;
    for (int i = 0; i < N; i++) {
        String name = Names.get(i);
        if (map.get(name) == null) {
            map.put(name,++id);
        }
    }

    // show result
    for (int i=0; i<N; i++) {
        String name = Names.get(i);
        System.out.println(map.get(name) + " " +name);
    }

}

Upvotes: 1

Trevor Bye
Trevor Bye

Reputation: 708

If I understand your question correctly, you ought to use a HashMap, as it will be a lot faster/easier than working with two arrays. I would do it like this:

Map<String,Integer> map = new HashMap<>();

This way you will be able to do map.put("name", int id), and it won't allow duplicate keys (key is the "name" in your case) so you will automatically have only one key/value pair for names that are the same.

Upvotes: 0

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