Dividing data into subsets

A common data-processing task is to divide a collection of data into subsets. In this recipe, we are going to explore standard library functions that allow us to buffer a collection into smaller chunks. Let's say we have a list containing a large number of Message type objects and we would like to transform it into collections of sub-lists of a constant size. For example, the transformation would take the original collection of n elements:

[mssg_1, mssg_2, mssg_3, mssg_4, mssg_5, mssg_6, mssg_7, ..., mssg_n]

And it would then split it into a collection of four element subsets:

[[mssg_1, mssg_2, mssg_3, mssg_4], ..., [mssg_n-3, mssg_n-2, mssg_n-1, mssg_n]]

Getting ready

Let's start by declaring the Message class that we are going to use in the following recipe:

data class Message(val text: String,
val time: Instant = Instant.now())

 

 

 

 

Let's declare the messages variable that stores the sample data:

val messages = listOf(
        Message("Any plans for the evening?"),
...