Summary - Lists

Combine mutableListOf, add and map to write a class list.

Summary: build a list, add, transform

In this summary you will combine mutableListOf, add and map to process a class list. First build a mutable list, add a new student, then upper-case every name with map.

val students = mutableListOf("Ava", "Liam")
students.add("Nora")
val big = students.map { it.uppercase() }
// [AVA, LIAM, NORA]

This chain shows both the mutable (add) and the transformable (map) side of lists.

Exercise Grow and transform the class list

Start with mutableListOf("Ava", "Liam"), add "Nora" with add, then upper-case every name with map { it.uppercase() } and print the result with println.

Show example solution

fun main() {
    val students = mutableListOf("Ava", "Liam")
    students.add("Nora")
    println(students.map { it.uppercase() })
}

Exercise Pick the long names with filter

Create a mutableListOf("Ava", "Liam", "Nora"). Use filter { it.length > 3 } to keep names longer than 3 characters and print the result with println.

Show example solution

fun main() {
    val students = mutableListOf("Ava", "Liam", "Nora")
    val longNames = students.filter { it.length > 3 }
    println(longNames)
}

Test yourself

Which chain works correctly?
- mutableListOf + add + filter { it.uppercase() }
- listOf + add + map { it.uppercase() }
- mutableListOf + put + map { it.uppercase() }
- mutableListOf + add + map { it.uppercase() }
Show answer

mutableListOf + add + map { it.uppercase() } — mutableListOf accepts add; map produces the upper-case list.
Match chain step to role

mutableListOf

Mutable start
add

Appends an element
map { }

Transforms each element
uppercase()

Upper-cases letters

Next lesson: Creating sets

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