[英]How can I design a Flow which is a average value of every latest 5 data of another Flow?
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.有一个 Flow 会每 100ms 发出一次数据,我希望得到 Flow 的每最新 5 个数据的平均值,并将平均值作为 Double 值转换为另一个 Flow。
How can I design the Flow?如何设计流程?
Code A代码 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:添加内容:
To plplmax: Thanks!致plplmax:谢谢!
I assume Code B will emit 1,2,3,4,5,6,7,8,9,10.....我假设代码 B 将发出 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, .... ?你保证代码 C 会先计算
(1+2+3+4+5)/5
,然后再计算(6+7+8+9+10)/5
秒,....? It's my expectation.这是我的期望。
I worry that Code C maybe calculate (1+2+3+4+5)/5
first, the calculate (2+3+4+5+6)/5
sencond, ...我担心代码 C 可能首先计算
(1+2+3+4+5)/5
,然后计算(2+3+4+5+6)/5
秒,...
Code B代码 B
suspend fun soundDbFlow(period: Long) = flow {
while (true) {
val data = getAmplitude()
emit(data)
delay(period)
}
}
Code C代码 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)
}
}
You can write a chunked operator like this:您可以像这样编写分块运算符:
/**
* 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:然后像这样使用它:
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) }
Is that what you want?那是你要的吗?
var result = 0
suspend fun soundDbFlow(period: Long) = flow {
while (true) {
val data = getAmplitude()
emit(data)
delay(period)
}
}
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)
}
}
private fun getAmplitude(): Int {
return ++result
}
private fun soundDb(input: Int, referenceAmp: Double = 1.0): Double {
return 20 * log10(input / referenceAmp)
}
fun main(): Unit = runBlocking {
reduceFlow().collect { println(it) }
}
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