Let’s understand the difference between Collections and Sequences with a simple example:

val operations = (1..10)
    .filter{it % 2 == 1}
    .map { it * 2 }
    .take(2)

Collections

In the above collection operations, we first loop through numbers from 1 to 10, then create a collection of numbers who are odd, then create another collection by multiplying the elements of previous collection by 2 and then create a collection by taking first 2 elements of previous collection.

For the above example with collections, the results at each step would be as follows:

val operations = (1..10) 
    .filter { it % 2 == 1 } // 1, 3, 5, 7, 9
    .map { it * 2 }        // 2, 6, 10, 14, 18
    .take(2)               // 2, 6

Now, let’s take a look at the map function for Collections.

#kotlin