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Kotlin Multiplatform Academy · Lesson

Operators: map, filter, combine

Transform and merge streams before the UI sees them.

Operators: map, filter, combine is a free Kotlin Multiplatform Academy lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Kotlin Multiplatform Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Shape the Stream

Raw streams rarely match what the UI wants. Operators let you transform a Flow on the way out, so the UI receives data already in the right shape.

Operators Are Lazy

Adding operators does not start any work. They build a new Flow that only runs when collected, keeping everything cold and efficient.

map Transforms Each Value

The map operator runs a function on every emitted value and emits the result. Great for converting one type into another.

numbers.map { n -> n * 2 }

filter Drops Values

Use filter to keep only the values you care about. Anything that fails the predicate is simply not emitted downstream.

numbers.filter { n -> n % 2 == 0 }

Chain Them Together

Operators compose top to bottom. You can chain filter then map to build a clean pipeline that reads like a sentence.

numbers
    .filter { it > 0 }
    .map { it.toString() }

combine Two Streams

The combine operator merges two flows. Whenever either one emits, you get the latest value from both, perfect for joined state.

combine(name, age) { n, a ->
    "$n is $a"
}

combine Waits for Both

combine emits nothing until both sources have produced a first value. After that, every change from either side triggers a fresh result.

Derive UI State

A common pattern is combining several state flows into one screen state. Your shared layer does the math, and the UI just renders the result.

distinctUntilChanged

To avoid repeating identical values, add distinctUntilChanged. It suppresses an emission that equals the previous one, sparing the UI extra work.

tags.distinctUntilChanged()

onEach for Side Peeks

Need to log or react without changing values? onEach runs an action for each emission and passes the value straight through.

result.onEach { log(it) }

All Multiplatform

Every one of these operators lives in kotlinx-coroutines and runs identically on Android and iOS. Build the pipeline once, share it everywhere. 🚀

Quick Check

Pick the right tool for the job.

Recap

You shaped streams with operators: map transforms, filter drops, and combine merges. Chained in shared code, they hand the UI ready-to-render data. 🚀

Frequently asked questions

Is the “Operators: map, filter, combine” lesson free?

Yes — the full text of “Operators: map, filter, combine” is free to read here on the web, and the Kotlin Multiplatform Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Kotlin Multiplatform Academy course, upgrade to CoddyKit PRO.

What will I learn in “Operators: map, filter, combine”?

Transform and merge streams before the UI sees them. You practise Kotlin Multiplatform Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Kotlin Multiplatform Academy?

No prior experience is required. Kotlin Multiplatform Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Operators: map, filter, combine” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Kotlin Multiplatform Academy lesson?

Yes. Every Kotlin Multiplatform Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Flow Basics in Shared Code
  2. StateFlow for Shared UI State
  3. Operators: map, filter, combine
  4. Collect Flows on Android & iOS
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