Kotlin partition() Method with Examples

In this article, we are going to discuss how to split the original collection into pair of collections, because sometimes while coding, you wish that you could just split a list into sublists without going into the for and while loops. Kotlin provides you with a function just for this occasion. In this article, we will see how to split a list based on some criteria. Suppose there is a list on which you need to perform an operation to segregate its items into two lists, one which agrees to some condition and the other which doesn’t. The typical way to do this is to run a loop over the collection object and add an if condition inside and segregate the object.

Kotlin has something in inbuild, which can make your life easier. There is an operator caller partition() that can segregate the list into two lists, one with the items matching the condition and another one with the non-matching condition, and the code will be like this:

Kotlin provides a partition function. According to the documentation of the partition function, it does the following, Splits the original array into a pair of lists, where the first list contains elements for which predicate yielded true, while the second list contains elements for which predicate yielded false.

Example 1:

In this example, we will create a list of numbers, and we want to split this list into two sublists: one having odd numbers and the other having even numbers:

Output:

( [2, 4, 6], [1, 3, 5])

As you can see in the preceding example, we need to put the condition in the predicate inside the partition block. The returned object is a Pair object, holding the two sublists. The partition function also works with the set collection in a similar way:

Output:

([2, 4, 6], [1, 3, 5])

Explanation:

Let’s take a look at the implementation of the partition function in Kotlin:

As you can see, the partition function is just an abstraction, that saves you from writing long for loops, but internally it does it the same old way.

Example 2:

The partition function works in a similar way with arrays as well. Here are its different usages. Each of them works similarly, just producing lists of different types: