Transforming with map & filter
Reshape values as they flow downstream.
Transforming with map & filter is a free SwiftUI Academy lesson on CoddyKit — lesson 2 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 SwiftUI Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Operators Reshape Streams
Between a publisher and its subscriber you can insert operators that transform values as they flow downstream.
map Transforms Each Value
The map operator runs a closure on every value and emits the result, changing the stream's shape.
[1, 2, 3].publisher
.map { $0 * 10 }map Can Change the Type
Because map returns whatever you want, the Output type can change, like turning numbers into strings.
[1, 2].publisher
.map { "Item \($0)" }filter Drops Values
The filter operator keeps only the values whose closure returns true and silently discards the rest.
[1, 2, 3, 4].publisher
.filter { $0 % 2 == 0 }Chaining Operators
Operators compose cleanly: chain filter then map to first narrow the stream, then reshape it.
.filter { $0 > 0 }
.map { $0 * 2 }Order Matters
Each operator sees only the output of the one above it, so reordering map and filter can quietly change your result.
compactMap Removes nil
Use compactMap when your transform may return nil, and Combine drops those empty results for you.
["1", "x", "3"].publisher
.compactMap { Int($0) }removeDuplicates
The removeDuplicates operator emits a value only when it differs from the previous one.
subject.removeDuplicates()scan Accumulates
The scan operator carries a running result, emitting an updated total for every value, like a live sum.
.scan(0) { total, next in total + next }Readable Pipelines
Reading top to bottom, a pipeline tells a story: this is where the declarative power of operators shines.
.filter { !$0.isEmpty }
.map { $0.uppercased() }Pure Transforms
Keep operator closures pure: avoid side effects so each value transforms predictably and tests stay simple.
Quick Check
A stream emits 1, 2, 3, 4. After .filter { $0 % 2 == 0 }.map { $0 * 10 }, what is emitted?
Recap: Shaping the Flow
You learned to reshape streams: map transforms, filter narrows, and compactMap clears out nil values. ✨
Frequently asked questions
Is the “Transforming with map & filter” lesson free?
Yes — the full text of “Transforming with map & filter” is free to read here on the web, and the SwiftUI 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 SwiftUI Academy course, upgrade to CoddyKit PRO.
What will I learn in “Transforming with map & filter”?
Reshape values as they flow downstream. You practise SwiftUI 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 SwiftUI Academy?
No prior experience is required. SwiftUI Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Transforming with map & filter” 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 SwiftUI Academy lesson?
Yes. Every SwiftUI 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
- Publishers & Subscribers
- Transforming with map & filter
- Debounce for Live Search
- Bridging Combine into SwiftUI