How can I design a Flow which is a average value of every latest 5 data of another Flow? - kotlin

Question

There is a Flow which will emit data every 100ms, and I hope to get a average value of every latest 5 data of the Flow, and convert the average value as Double value into another Flow.
How can I design the Flow?
Code A
fun soundDbFlow(period: Long = 100) = flow {
while (true) {
var data = getAmplitude()
emit(data)
delay(period)
}
}
.get_Average_Per5_LatestData {...} //How can I do? or is there other way?
.map { soundDb(it) }
private fun getAmplitude(): Int {
var result = 0
mRecorder?.let {
result = it.maxAmplitude
}
return result
}
private fun soundDb(input:Int, referenceAmp: Double = 1.0): Double {
return 20 * Math.log10(input / referenceAmp)
}
Added Content:
To plplmax: Thanks!
I assume Code B will emit 1,2,3,4,5,6,7,8,9,10.....
Do you guarantee Code C will calculate (1+2+3+4+5)/5 first, then calculate (6+7+8+9+10)/5 second, .... ? It's my expectation.
I worry that Code C maybe calculate (1+2+3+4+5)/5 first, the calculate (2+3+4+5+6)/5 sencond, ...
Code B
suspend fun soundDbFlow(period: Long) = flow {
while (true) {
val data = getAmplitude()
emit(data)
delay(period)
}
}
Code C
private fun reduceFlow(period: Long = 100) = flow {
while (true) {
val result = soundDbFlow(period)
.take(5)
.map { soundDb((it / 5.0).roundToInt()) }
.reduce { accumulator, value -> accumulator + value }
emit(result)
}
}

Answer 1

You can write a chunked operator like this:
/**
* Returns a Flow that emits sequential [size]d chunks of data from the source flow,
* after transforming them with [transform].
*
* The list passed to [transform] is transient and must not be cached.
*/
fun <T, R> Flow<T>.chunked(size: Int, transform: suspend (List<T>)-> R): Flow<R> = flow {
val cache = ArrayList<T>(size)
collect {
cache.add(it)
if (cache.size == size) {
emit(transform(cache))
cache.clear()
}
}
}
And then use it like this:
suspend fun soundDbFlow(period: Long) = flow {
while (true) {
val data = getAmplitude()
emit(data)
delay(period)
}
}
.chunked(5) { (it.sum() / 5.0).roundToInt() }
.map { soundDb(it) }

Answer 2

Is that what you want?
var result = 0
fun soundDbFlow(period: Long) = flow {
while (true) {
delay(period)
val data = getAmplitude()
emit(data)
}
}
fun reduceFlow(period: Long = 100) = flow {
while (true) {
val sum = soundDbFlow(period)
.take(5)
.reduce { accumulator, value -> accumulator + value }
val average = (sum / 5.0).roundToInt()
emit(soundDb(average))
}
}
fun getAmplitude(): Int {
return ++result
}
fun soundDb(input: Int, referenceAmp: Double = 1.0): Double {
return 20 * log10(input / referenceAmp)
}
fun main(): Unit = runBlocking {
reduceFlow().collect { println(it) }
}