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Kotlin Academy · Lesson

combine and zip: Merging Multiple Flows

Combine multiple Flows and zip their emissions together.

Why Merge Flows?

Real apps often need to combine multiple data streams: user preferences + network data, form fields + validation state. Kotlin Flow provides zip, combine, and merge for this.

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*
fun main() = runBlocking {
    val names = flowOf("Alice", "Bob", "Carol")
    val ages  = flowOf(30, 25, 35)
    names.zip(ages) { name, age -> "$name is $age" }
         .collect { println(it) }
}

zip: Paired Emissions

zip pairs emissions one-to-one in order. It stops when the shorter flow ends.

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*
fun main() = runBlocking {
    val a = flowOf(1, 2, 3, 4)   // 4 elements
    val b = flowOf("a", "b", "c")  // 3 elements — zip stops here
    a.zip(b) { n, s -> "$n-$s" }
     .collect { println(it) } // 1-a, 2-b, 3-c
}

All lessons in this course

  1. Flow Operators: map, filter, transform, and take
  2. catch and onCompletion: Error Handling in Flow
  3. combine and zip: Merging Multiple Flows
  4. flowOn and buffer: Context and Backpressure
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