Removing duplicates from an Array that contains multiple String elements

Question

I want to remove duplicate String values inside my String[], but I am not sure quite how to do that.

Heres an example:

public static void main(String[] args){

  String[] listofWords = new String [5];
  listofWords[0]  = "BMW";
  listofWords[1]  = "Audi";
  listofWords[2]  = "Mercedes";
  listofWords[3]  = "Audi";
  listofWords[4]  = "BMW";
  for(int i = 0; i<listofWords.length-1; i++){
    system.out.println(listofWords[i]);
  }
}

How would I got about deleting the duplicates in this array and only have one of each make?

Answer 1

You can convert your String[] to Set:

String [] listofWords = new String [5];
listofWords [0]  = "BMW";
listofWords [1]  = "Audi";
listofWords [2]  = "Mercedes";
listofWords [3]  = "Audi";
listofWords [4]  = "BMW";

Set<String> set = new HashSet<String>(Arrays.asList(listofWords));
System.out.println(set); //prints [Audi, Mercedes, BMW]

You can convert the Set back to String[] like this:

listofWords = set.toArray(new String[set.size()]);

Answer 2

1. If memory is not a concern, convert to a set and back to array, like:

   Set<String> mySet = new HashSet<String>(Arrays.asList(listofWords));
   listofWords = mySet.toArray(new String[mySet.size()]);
   

2. If you have memory limits then you should sort the array:

   Arrays.sort(listofWords);
   

   Then remove the duplicates, like this:

   public static int removeDuplicates(String[] A) {
     int length=A.length;
     if(length==0 || length==1) return length;
     int i=1;
     for(int j=1; j<length; j++){
       if(!A[j].equals(A[j-1])){
          A[i]=A[j];
         i++;
       }
     }
     if(i<length) A[i]=null;
       return i;
   }
   

   This method will remove the duplicates and return the new array size.

   Eg.

   public static void main(String[] args) {
     String[] listofWords = new String [5];
     listofWords[0]  = "BMW";
     listofWords[1]  = "Audi";
     listofWords[2]  = "Mercedes";
     listofWords[3]  = "Audi";
     listofWords[4]  = "BMW";
     Arrays.sort(listofWords);
     int n=removeDuplicates(listofWords);
     for(int i = 0; i<n; i++){
       System.out.println(listofWords[i]);
     }
   }
   

Answer 3

I would recommend this solution using Java 8 streams

String[] result = Arrays.stream(listofWords).distinct().toArray(s -> new String[s]);

This also addresses the memory concerns you have expressed in the comments. It will just create an array with enough size to store distinct values and store the result there.

As a side note you could have initialized listofWords more easily like this

String[] listofWords = {"BMW", "Audi", "Mercedes", "Audi", "BMW"};

Answer 4

//JAVA-8 - Remove Duplicates

    List li1 = new ArrayList<>(Arrays.asList(10, 22, 10, 20, 11, 22));
    
    System.out.println("Duplicate elements: " + li1);
    
    // Create new list from elements of original list
    List li2 = (List) li1.stream().distinct().collect(Collectors.toList());
    
    // ArrayList with duplicates removed
    System.out.println("Non-duplicate elements: " + li2);

Answer 5

It is straightforward to do in-place if you don't need to preserve the order of appearance in the array: sort the array first and use two pointers to iterate through the array:

Arrays.sort(listofWords);
int i = 0, j = 0;
while (j < listofWords.length) {
  // Copy the element from the j-th position to the i-th position.
  listofWords[i] = listofWords[j];
  // Increment j while the word at position j equals the word at position i.
  while (j < listofWords.length && listofWords[j].equals(listofWords[i])) {
    ++j;
  }
  // Increment i, to be the next unique element index.
  ++i;
}

// i currently points to the element after the last non-duplicate element, so
// ideally we would throw away elements [i..listofWords.length)
// However, you can't resize an array in Java.
// This loop just nulls out the remaining elements, since their contents are all
// already in the array.
while (i < listofWords.length) {
  listofWords[i++] = null;
}

Answer 6

You can try the below solution :

public static void main(String[] args) {

    String strArray[] =  new String[]{"bmw","audi","bmw","honda","Yamaha","Yamaha","maruti","hyundai","hyundai"};

    HashSet setOfStrings= new HashSet<String>();
    for(int i=0;i<strArray.length;i++){
        boolean result=setOfStrings.add(strArray[i]);
        if(!result){
            System.out.println("duplicate elements include...."+strArray[i]); 
           }
    }
    Object[] newString= new Object[strArray.length];
    newString=setOfStrings.toArray();
    System.out.println("Array without Duplicates......."+Arrays.toString(newString));
}

Answer 7

import java.util.Arrays;

/**
 * @author Kishore Diyyana
 * Simple Bruteforce approach
 */
public class RemoveDupilcates {

    public static void main(String[] args) {

        RemoveDupilcates removeDups = new RemoveDupilcates();

        removeDups.removeDups();

    }

    public void removeDups() {
        int[] numbers = new int[] {10, 22, 10, 20, 11, 22};
        int[] temp = new int [numbers.length];
        int count = -1;
        for (int i=0; i<numbers.length;i++) {
            boolean hasFound = false;
            for (int j = i+1; j< numbers.length; j++) {
                if (numbers[i] == numbers[j]) {
                    hasFound = true;
                    break;
                }
            }
            if (!hasFound) {
                count++;
                System.out.println(numbers[i]);
                temp[count] = numbers[i];
            }
        }
        int[] outpout = null;
        if (count < numbers.length) {
            outpout = new int [count];
            System.arraycopy(temp, 0, outpout, 0, count);
        }
        System.out.println(Arrays.toString(outpout));
    }
}