Flow operators (map, filter, transform) in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the map operator do in a Kotlin Flow?

The map operator transforms each emitted value from the flow by applying a given function, producing a new flow with the transformed values.

beginner

How does the filter operator work in a Kotlin Flow?

The filter operator lets only those values pass through the flow that satisfy a given condition (predicate). Values that don't meet the condition are skipped.

intermediate

Explain the difference between map and transform operators in Kotlin Flow.

map applies a simple one-to-one transformation on each value. transform is more flexible; it can emit zero, one, or many values for each input and can run suspend functions inside.

intermediate

Can transform operator emit multiple values for a single input in Kotlin Flow?

Yes, transform can emit zero, one, or multiple values for each input value, making it very flexible for complex transformations.

advanced

What is the role of suspend functions inside the transform operator?

Inside transform, you can call suspend functions to perform asynchronous or long-running operations before emitting values, which is not possible with map.

Which Flow operator would you use to change each emitted value to its uppercase string?

A map

B filter

C transform

D collect

The map operator transforms each emitted value, such as converting strings to uppercase.

What does the filter operator do in a Kotlin Flow?

A Transforms values

B Emits multiple values per input

C Emits only values that satisfy a condition

D Collects values

filter lets only values that meet a condition pass through.

Which operator allows emitting multiple values for a single input in Kotlin Flow?

A map

B filter

C take

D transform

transform can emit zero, one, or many values per input.

Can you call suspend functions inside the map operator?

A Yes, always

B No, <code>map</code> does not support suspend functions

C Only if wrapped in <code>withContext</code>

D Only for filtering

map does not support suspend functions; use transform for that.

Which operator would you use to skip values that are less than 10 in a Flow?

A filter

B map

C transform

D reduce

filter is used to skip values that don't meet a condition.

Describe how the map, filter, and transform operators work in Kotlin Flow and when you might use each.

Think about simple vs complex transformations and filtering.

Explain why you might choose transform over map in a Kotlin Flow.

Consider asynchronous operations and multiple emissions.