Sequence operators (map, filter) in Kotlin - Mini Project: Build & Apply

Using Sequence Operators: map and filter in Kotlin

📖 Scenario: You are working on a simple Kotlin program that processes a list of ages to find which people are adults and then convert their ages to a string format for display.

🎯 Goal: Build a Kotlin program that uses sequence operators map and filter to select adults (age 18 or older) from a list of ages and then convert those ages to strings.

📋 What You'll Learn

Create a list of ages with exact values

Create a sequence from the list

Use filter to keep only ages 18 or older

Use map to convert the filtered ages to strings

Print the resulting list of strings

💡 Why This Matters

🌍 Real World

Filtering and transforming data is common in apps that process user information, like showing only adult users or formatting data for display.

💼 Career

Understanding sequence operators like <code>map</code> and <code>filter</code> is essential for Kotlin developers working on data processing, Android apps, or backend services.

1

Create the list of ages

Create a list called ages with these exact integer values: 15, 22, 17, 30, 14, 19.

Kotlin

# Create the list of ages
# Your code here

Need a hint?

Use listOf to create the list with the exact numbers.

2

Create a sequence from the list

Create a variable called ageSequence by calling asSequence() on the ages list.

Kotlin

val ages = listOf(15, 22, 17, 30, 14, 19)
# Create a sequence called ageSequence from ages
# Your code here

Need a hint?

Use asSequence() on the ages list to create a sequence.

3

Filter adults and map to strings

Create a variable called adultAgesStrings by applying filter on ageSequence to keep ages 18 or older, then apply map to convert each age to a string, and finally convert the result to a list using toList().

Kotlin

val ages = listOf(15, 22, 17, 30, 14, 19)
val ageSequence = ages.asSequence()
# Filter ages 18 or older and map to strings, then convert to list
# Your code here

Need a hint?

Use filter { it >= 18 } to keep adults, then map { it.toString() } to convert to strings, and toList() to get a list.

4

Print the resulting list

Write a println statement to print the adultAgesStrings list.

Kotlin

val ages = listOf(15, 22, 17, 30, 14, 19)
val ageSequence = ages.asSequence()
val adultAgesStrings = ageSequence.filter { it >= 18 }.map { it.toString() }.toList()
# Print the adultAgesStrings list
# Your code here

Need a hint?

Use println(adultAgesStrings) to display the list.