Removing Duplicate Values from ArrayList

Question

I have one Arraylist of String and I have added Some Duplicate Value in that. and i just wanna remove that Duplicate value So how to remove it.

Here Example I got o

Answer 1

Simple function for removing duplicates from list

private void removeDuplicates(List<?> list)
{
    int count = list.size();

    for (int i = 0; i < count; i++) 
    {
        for (int j = i + 1; j < count; j++) 
        {
            if (list.get(i).equals(list.get(j)))
            {
                list.remove(j--);
                count--;
            }
        }
    }
}

Example:
Input: [1, 2, 2, 3, 1, 3, 3, 2, 3, 1, 2, 3, 3, 4, 4, 4, 1]
Output: [1, 2, 3, 4]

Answer 2

public static List<String> removeDuplicateElements(List<String> array){
    List<String> temp = new ArrayList<String>();
    List<Integer> count = new ArrayList<Integer>();
    for (int i=0; i<array.size()-2; i++){
        for (int j=i+1;j<array.size()-1;j++)
            {
                if (array.get(i).compareTo(array.get(j))==0) {
                    count.add(i);
                    int kk = i;
                }
            }
        }
        for (int i = count.size()+1;i>0;i--) {
            array.remove(i);
        }
        return array;
    }
}

Answer 3

Java 8 stream function

You could use the distinct function like above to get the distinct elements of the list,

stringList.stream().distinct();

From the documentation,

Returns a stream consisting of the distinct elements (according to Object.equals(Object)) of this stream.

---

Another way, if you do not wish to use the equals method is by using the collect function like this,

stringList.stream()  
    .collect(Collectors.toCollection(() -> 
        new TreeSet<String>((p1, p2) -> p1.compareTo(p2)) 
));  

From the documentation,

Performs a mutable reduction operation on the elements of this stream using a Collector.

Hope that helps.

Answer 4

It is better to use HastSet

1-a) A HashSet holds a set of objects, but in a way that it allows you to easily and quickly determine whether an object is already in the set or not. It does so by internally managing an array and storing the object using an index which is calculated from the hashcode of the object. Take a look here

1-b) HashSet is an unordered collection containing unique elements. It has the standard collection operations Add, Remove, Contains, but since it uses a hash-based implementation, these operation are O(1). (As opposed to List for example, which is O(n) for Contains and Remove.) HashSet also provides standard set operations such as union, intersection, and symmetric difference.Take a look here

2) There are different implementations of Sets. Some make insertion and lookup operations super fast by hashing elements. However that means that the order in which the elements were added is lost. Other implementations preserve the added order at the cost of slower running times.

The HashSet class in C# goes for the first approach, thus not preserving the order of elements. It is much faster than a regular List. Some basic benchmarks showed that HashSet is decently faster when dealing with primary types (int, double, bool, etc.). It is a lot faster when working with class objects. So that point is that HashSet is fast.

The only catch of HashSet is that there is no access by indices. To access elements you can either use an enumerator or use the built-in function to convert the HashSet into a List and iterate through that.Take a look here

Answer 5

public static void main(String[] args) {
    @SuppressWarnings("serial")
    List<Object> lst = new ArrayList<Object>() {
        @Override
        public boolean add(Object e) {
            if(!contains(e))
            return super.add(e);
            else
            return false;
        }
    };
    lst.add("ABC");
    lst.add("ABC");
    lst.add("ABCD");
    lst.add("ABCD");
    lst.add("ABCE");
    System.out.println(lst);

}

This is the better way

Answer 6

 public void removeDuplicates() {
    ArrayList<Object> al = new ArrayList<Object>();
    al.add("java");
    al.add('a');
    al.add('b');
    al.add('a');
    al.add("java");
    al.add(10.3);
    al.add('c');
    al.add(14);
    al.add("java");
    al.add(12);

    System.out.println("Before Remove Duplicate elements:" + al);
    for (int i = 0; i < al.size(); i++) {
        for (int j = i + 1; j < al.size(); j++) {
            if (al.get(i).equals(al.get(j))) {
                al.remove(j);
                j--;
            }
        }
    }
    System.out.println("After Removing duplicate elements:" + al);
}

Before Remove Duplicate elements:

[java, a, b, a, java, 10.3, c, 14, java, 12]

After Removing duplicate elements:

[java, a, b, 10.3, c, 14, 12]