Convert stream or sequence to a stream or sequence of summaries-CodePudding

Using Kotlin, how would I transform a Sequence of detail objects into a Sequence of summary objects, where each summary object represents a fixed number of detailed objects? It's kind of like map, except it's not one-to-one and it's kind of like reduce except it's not to a single accumulator?

For example:

var hourlyInfo: Sequence<HourlyData> = ...
var dailyInfo: Sequence<DailySummary> = hourlyInfo.somethingMagical()

What about the same problem with a stream instead of a sequence?

CodePudding user response：

If there's a known fixed number of items, you use chunked and then map. When the sequence is iterated, actual lists of each chunk of items will be allocated.

var dailyInfo: Sequence<DailySummary> = hourlyInfo
  .chunked(12)
  .map(::DailySummary) // for example if it has a constructor taking a List of 12 HourlyData

If the List of HourlyData isn't ordered, or there isn't some fixed size, then I suppose you have to group by some property in HourlyData and then map it. This does not preserve Sequence status.

var dailyInfo: Sequence<DailySummary> = hourlyInfo
  .groupBy(HourlyData::hourOfDay)
  .map { (hour, listOfHourlyData) -> DailySummary(hour, listOfHourlyData) }