Why sequences matter for performance in Kotlin - See It in Action

Why sequences matter for performance

📖 Scenario: You are working with a list of numbers and want to perform multiple operations on them. You want to understand how using sequences can improve performance by processing elements lazily, instead of creating intermediate collections.

🎯 Goal: Build a Kotlin program that compares processing a list with normal collection operations versus using sequences, to see how sequences can improve performance.

📋 What You'll Learn

Create a list of integers from 1 to 1,000,000

Create a variable to hold a threshold value of 1000

Use normal collection operations to filter numbers greater than the threshold and map them by multiplying by 2

Use sequence operations to do the same filtering and mapping

Print the size of the resulting lists from both methods

💡 Why This Matters

🌍 Real World

Sequences help when working with large data sets or chains of operations, making programs faster and using less memory.

💼 Career

Understanding sequences is important for Kotlin developers to write efficient and performant code, especially in data processing and backend applications.

1

Create the list of numbers

Create a list called numbers containing integers from 1 to 1_000_000 using (1..1_000_000).toList().

Kotlin

# Create the list of numbers
# Your code here

Need a hint?

Use Kotlin's range and toList() to create the list.

2

Set the threshold value

Create an integer variable called threshold and set it to 1000.

Kotlin

val numbers = (1..1_000_000).toList()
# Create the threshold variable
# Your code here

Need a hint?

Just create a simple integer variable.

3

Filter and map using collections and sequences

Create a list called filteredMappedList by filtering numbers for values greater than threshold and then mapping each value to its double using normal collection operations. Then create a sequence called filteredMappedSequence by converting numbers to a sequence, applying the same filter and map operations.

Kotlin

val numbers = (1..1_000_000).toList()
val threshold = 1000
# Create filteredMappedList using filter and map on numbers
# Create filteredMappedSequence using asSequence(), filter, and map
# Your code here

Need a hint?

Use filter and map on the list and on the sequence.

4

Print the sizes of the results

Print the size of filteredMappedList and the size of filteredMappedSequence converted to a list using toList(). Use println for both.

Kotlin

val numbers = (1..1_000_000).toList()
val threshold = 1000

val filteredMappedList = numbers.filter { it > threshold }.map { it * 2 }
val filteredMappedSequence = numbers.asSequence().filter { it > threshold }.map { it * 2 }
# Print the size of filteredMappedList
# Print the size of filteredMappedSequence converted to list
# Your code here

Need a hint?

Use println(filteredMappedList.size) and println(filteredMappedSequence.toList().size).