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How to remove duplicates from an ArrayList in Kotlin

How to remove duplicates from an ArrayList in Kotlin.

Here's a step-by-step tutorial on how to remove duplicates from an ArrayList in Kotlin:

Step 1: Create an ArrayList​

First, let's create an ArrayList with some duplicate elements. For example, let's say we have an ArrayList of Integers:

val numbers = arrayListOf(1, 2, 3, 4, 3, 2, 1)

Step 2: Use distinct() function​

In Kotlin, you can use the distinct() function to remove duplicates from a list. This function returns a new list containing only the distinct elements from the original list.

val distinctNumbers = numbers.distinct()

After executing this code, distinctNumbers will contain [1, 2, 3, 4], which is the original list with duplicates removed.

Step 3: Use distinctBy() function​

If you have a custom object in your ArrayList and want to remove duplicates based on a specific property of the object, you can use the distinctBy() function. This function takes a lambda expression that specifies the property to use for checking uniqueness.

For example, let's say we have a list of Person objects with name and age properties:

data class Person(val name: String, val age: Int)

val people = arrayListOf(
    Person("John", 25),
    Person("Jane", 30),
    Person("John", 25),
    Person("Alice", 35)
)

To remove duplicates based on the name property, we can use the distinctBy() function:

val distinctPeople = people.distinctBy { it.name }

After executing this code, distinctPeople will contain only the unique Person objects based on their name property.

Step 4: Use HashSet​

Another way to remove duplicates from an ArrayList is by using a HashSet. A HashSet is a collection that contains no duplicate elements.

val numbers = arrayListOf(1, 2, 3, 4, 3, 2, 1)
val distinctNumbers = HashSet(numbers)

After executing this code, distinctNumbers will contain [1, 2, 3, 4], which is the original list with duplicates removed.

Step 5: Use a loop​

If you prefer a more manual approach, you can use a loop to iterate over the ArrayList and remove duplicates manually.

val numbers = arrayListOf(1, 2, 3, 4, 3, 2, 1)
val distinctNumbers = ArrayList<Int>()

for (number in numbers) {
    if (!distinctNumbers.contains(number)) {
        distinctNumbers.add(number)
    }
}

After executing this code, distinctNumbers will contain [1, 2, 3, 4], which is the original list with duplicates removed.

That's it! You now know several ways to remove duplicates from an ArrayList in Kotlin. Choose the method that suits your needs best.