Filter and filterNot in Kotlin - Mini Project: Build & Apply

Filter and filterNot

📖 Scenario: You are managing a list of products in a store. Some products are on sale, and you want to separate the sale items from the regular items.

🎯 Goal: Build a Kotlin program that uses filter and filterNot to create two lists: one with products on sale and one with products not on sale.

📋 What You'll Learn

Create a list of products with their sale status

Create a variable to hold the sale status to filter by

Use filter to get products on sale

Use filterNot to get products not on sale

Print both filtered lists

💡 Why This Matters

🌍 Real World

Filtering lists is common when you want to separate data based on conditions, like showing only available products or filtering messages.

💼 Career

Understanding how to filter collections is important for data processing, user interface updates, and backend logic in many programming jobs.

1

Create the product list

Create a list called products with these exact entries: "Shoes" to true, "Hat" to false, "Jacket" to true, "Socks" to false.

Kotlin

# Create the list of products with sale status
# Your code here

Need a hint?

Use listOf with pairs like "Name" to Boolean.

2

Set the sale filter

Create a Boolean variable called onSale and set it to true.

Kotlin

val products = listOf("Shoes" to true, "Hat" to false, "Jacket" to true, "Socks" to false)
# Create a Boolean variable called onSale and set it to true
# Your code here

Need a hint?

Just write val onSale = true.

3

Filter products on sale and not on sale

Create a list called saleItems by filtering products where the second value equals onSale. Then create a list called regularItems by filtering products where the second value does NOT equal onSale using filterNot.

Kotlin

val products = listOf("Shoes" to true, "Hat" to false, "Jacket" to true, "Socks" to false)
val onSale = true
# Create saleItems using filter where second equals onSale
# Create regularItems using filterNot where second equals onSale
# Your code here

Need a hint?

Use filter and filterNot with it.second == onSale.

4

Print the filtered lists

Print saleItems and regularItems each on its own line.

Kotlin

val products = listOf("Shoes" to true, "Hat" to false, "Jacket" to true, "Socks" to false)
val onSale = true
val saleItems = products.filter { it.second == onSale }
val regularItems = products.filterNot { it.second == onSale }
# Print saleItems
# Print regularItems
# Your code here

Need a hint?

Use println(saleItems) and println(regularItems).