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How to sort an ArrayList in Kotlin

How to sort an ArrayList in Kotlin.

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

Step 1: Create an ArrayList​

First, you need to create an ArrayList of elements that you want to sort. You can do this by declaring a variable of type ArrayList and initializing it with some values. For example:

val numbers = arrayListOf(5, 2, 9, 1, 7)

Step 2: Sort the ArrayList in ascending order​

To sort the ArrayList in ascending order, you can use the sort() function. This function sorts the elements of the ArrayList in-place. Here's an example:

numbers.sort()

After calling the sort() function, the elements in the numbers ArrayList will be sorted in ascending order.

Step 3: Sort the ArrayList in descending order​

If you want to sort the ArrayList in descending order, you can use the sortDescending() function. This function sorts the elements of the ArrayList in descending order. Here's an example:

numbers.sortDescending()

After calling the sortDescending() function, the elements in the numbers ArrayList will be sorted in descending order.

Step 4: Sort the ArrayList using a custom comparator​

Sometimes, you may want to sort the elements of the ArrayList based on a custom criteria. In such cases, you can use the sortWith() function and provide a custom comparator. The comparator is a function that takes two elements of the ArrayList and compares them. Here's an example:

val personList = arrayListOf(
    Person("John", 25),
    Person("Alice", 30),
    Person("Bob", 20)
)

personList.sortWith(compareBy { it.age })

In the example above, we have an ArrayList of Person objects. We want to sort the ArrayList based on the age property of the Person objects. We use the compareBy() function to create a comparator that compares the age property. Then, we pass this comparator to the sortWith() function to sort the personList ArrayList based on the age property.

Step 5: Sort the ArrayList using a custom sorting order​

If you want to sort the elements of the ArrayList based on a custom sorting order, you can use the sortBy() or sortByDescending() functions and provide a lambda expression or a property reference. Here's an example:

val fruits = arrayListOf("apple", "banana", "cherry", "date")

fruits.sortBy { it.length }

In the example above, we have an ArrayList of fruit names. We want to sort the ArrayList based on the length of the fruit names. We use the sortBy() function and provide a lambda expression { it.length } that returns the length of each fruit name. This lambda expression is used to determine the sorting order.

That's it! You now know how to sort an ArrayList in Kotlin.