Scala 中的尾递归用例解决方案 [英] Tail Recursion Use Case Solution in Scala
问题描述
我正在尝试使用尾递归解决问题.用例是:
I am trying to solve a problem using tail recursion. The use case is:
我有文件夹列表,每个文件夹都有文件列表,每个文件都有几条记录.我想对记录进行一些转换并将它们批量写入 kinesis.
val listOfFolders = Folder1(File1(RF11, RF12, RF13), File2(RF21,RF22))
我想在 kinesis 中一次写两个记录.到目前为止,我已经尝试过:
I want to write let's say two records at a time in kinesis. So far I have tried:
listOfFolders.map { folder =>
val files = fetchAllFilesFromFolder(folder)
if (files.nonEmpty) {
sendBatch(files, Seq.empty[(ByteBuffer, String)], 2)
} else {
logger.info(s"No files are present in folder")
}
}
@scala.annotation.tailrec
def sendBatch(
files: Seq[Files],
buffer: Seq[(ByteBuffer, String)],
numberOfRecordsToSend: Int
): Unit =
files match {
case Nil => {
if (buffer.nonEmpty) {
sendToKinesis(streamName, buffer) map { putDataResult =>
val putDataList = putDataResult.getRecords.asScala.toList
logger.info(
s"Successfully Sent"
)
}
} else {
logger.info(s"Successfully sent")
}
}
case head :: tail => {
val fileData = readFileData()
val byteData: Seq[(ByteBuffer, String)] = transformDataAndConvertToByteBuffer(fileData)
val currentBatch = buffer ++ byteData
if (currentBatch.size >= numberOfRecordsToSend) {
sendToKinesis(streamName, buffer) map { putRecordRes =>
val putDataList = putRecordRes.getRecords.asScala.toList
logger.info(
s"Sent successfully"
)
}
sendBatch(tail, Seq.empty[(ByteBuffer, String)], 2)
} else {
sendBatch(tail, currentBatch, 2)
}
}
}
sendToKinesis 使用 KCL putRecords.
sendToKinesis uses KCL putRecords.
上面代码的问题是:
从一个文件中读取所有数据.所以如果文件有 5 条记录将发送kinesis 有 5 条记录,但批量大小为 2.
Reads all the data from one file. So if file has 5 records will send 5 records to kinesis but the batch size is 2.
无法从地图调用尾递归方法.
Can't call the tail recursive method from map.
如果 - 如果文件 1 有 3 条记录,则应注意发送 2 条记录将 RF11、RF12 一起记录,然后将 RF13、RF21 一起记录,最后RF22.
Also to be taken care if - If file1 has 3 records it should send 2 records RF11, RF12 together and then RF13,RF21 together and at last RF22.
我不想在我的代码中使用任何 var.可以用tail rec解决吗?
I do not want to use any var in my code. Can it be solved using the tail rec?
推荐答案
你有两个子问题
- 如何发送固定大小的批次
@scala.annotation.tailrec
def sendBatch(file: Option[File], buffer: Seq[(ByteBuffer, String)], numbersOfRecrodsToSend: Int): Seq[(ByteBuffer, String)] = {
if (buffer.length < numbersOfRecrodsToSend) {
// case 1: too few records to be sent
file match {
// case 1.1: file was not yet read
case Some(f) => sendBatch(None, buffer ++ getByteData(f), numbersOfRecrodsToSend)
// case 1.2: too few records, file was already read, return leftover records
case None => buffer
}
} else {
// case 2: we can send numbersOfRecrodsToSend to Kinesis
val (toSend, newBuffer) = buffer.splitAt(numbersOfRecrodsToSend)
sendToKinesis(streamName, toSend)
sendBatch(file, newBuffer, numbersOfRecrodsToSend)
}
}
- 如何遍历列表并发送固定大小的批次
// start with empty list of files to send and for each folder
// add it's files to the buffer and send as many records as you can
// the leftover is going to be passed to next iteration for both files and directories
val partial = listOfFolders.foldLeft(Seq.empty[(ByteBuffer, String)]) { case (acc, folder) =>
fetchAllFilesFromFolder(folder).foldLeft(acc) { case (acc2, file) =>
sendBatch(Some(file), acc2, numbersOfRecrodsToSend)
}
}
// if any records have left - send them too
if (partial.nonEmpty) {
sendToKinesis(streamName, partial)
}
<小时>
希望你有这个想法.
Hopefully you got the idea.
这篇关于Scala 中的尾递归用例解决方案的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!