How to Remove duplicates from array ?

Remove duplicates in array ?

There are different ways we can remove duplicates in array. By using Set, LinkedHashset, Streams etc.,. we can remove duplicates in array.

import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

public class removeArrayDuplicates {

    public static void main(String[] args) {
    int a[] = { 10, 20, 30, 40, 50, 10, 20, 30 };

    Set<Integer> s = new HashSet<>();

    for (int arrayValue : a) {
    s.add(arrayValue);
   }
   System.out.println("Final array with unique values using set=" + s);

   System.out.println("<<----------------------------------------------->>");

   Set<Integer> ns = new LinkedHashSet<>();

   for (int arrayValue : a) {
    ns.add(arrayValue);
  }
  System.out.println("Final array with unique values using Linked Hash Set=" + ns);

  System.out.println("<<----------------------------------------------->>");

  List<Integer> list = Arrays.stream(a).distinct().boxed().collect(Collectors.toList());
  System.out.println("Final array with unique values using streams=" + list);

  System.out.println("<<----------------------------------------------->>");
  }

}

Output:

remove duplicates from array in java

We can also remove duplicate from array using for loop as well.

import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.stream.Collectors;

public class removeArrayDuplicates {
    public static void main(String[] args) {
    int a[] = { 10, 20, 30, 40, 50, 10, 20, 30 };
    System.out.println("<<----------------------------------------------->>");
    Arrays.sort(a);
    System.out.print("Sorted array=");
    for (int y = 0; y < a.length; y++) {
    System.out.print(a[y] + " ");
    }
    int[] temp = new int[a.length];
    int k = 0;
    for (int i = 0; i < a.length - 1; i++) {
        if (a[i] != a[i + 1]) {
            temp[k] = a[i];
            k++;
        }
    }
    temp[k] = a[a.length - 1];
    System.out.println();
    System.out.print("Final Unique values in array using for loop=");
    for (int e = 0; e <= k; e++) {
        System.out.print(temp[e] + " ");
    }
 }
}

Output:

We can also remove duplicate from array using HashMap keySet(),EntrySet().

import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class removeArrayDuplicates {
    public static void main(String[] args) {
    int a[] = { 10, 10, 20, 30, 40, 50, 10, 20, 30 };
    Map<Integer, Integer> hm = new HashMap<Integer, Integer>();
    for (int n : a) {
        if (!hm.containsKey(n)) {
            hm.put(n, 1);
        } else {
            hm.put(n, hm.get(n) + 1);
        }
    }
    System.out.println("Hash map=" + hm);
    System.out.println("<<----------------------------------------------->>");
    Set<Entry<Integer, Integer>> entries = hm.entrySet();
    System.out.print("Final duplicate values using Hash map entry Set=");
    for (Entry<Integer, Integer> entry : entries) {
    if (entry.getValue() > 1) {
        System.out.print(entry.getKey() + " ");
        }
    }
    System.out.println();
    System.out.print("Final unique values using Hash map entry Set=");
    for (Entry<Integer, Integer> entry : entries) {
    if (entry.getValue() <= 1) {
        System.out.print(entry.getKey() + " ");
        }
    }
    System.out.println();
    System.out.println("<<----------------------------------------------->>");
    System.out.println("Hash map=" + hm);
    Set<Integer> hashKeys = hm.keySet();
    System.out.print("Final duplicate values using Hash map keySet()=");
    for (int key : hashKeys) {
        if (hm.get(key) > 1) {
            System.out.print(key + " ");
        }
    }
    System.out.println();
    System.out.print("Final unique values using Hash map keySet()=");
    for (int key : hashKeys) {
        if (hm.get(key) <= 1) {
            System.out.print(key + " ");
        }
    }
  }
}

Output:

Please comment below to feedback or ask questions.