Scala collection of dates and group by week - scala

Question

import java.time.LocalDate
case class Day(date: LocalDate, other: String)
val list = Seq(
Day(LocalDate.of(2016, 2, 1), "text"),
Day(LocalDate.of(2016, 2, 2), "text"), // Tuesday
Day(LocalDate.of(2016, 2, 3), "text"),
Day(LocalDate.of(2016, 2, 4), "text"),
Day(LocalDate.of(2016, 2, 5), "text"),
Day(LocalDate.of(2016, 2, 6), "text"),
Day(LocalDate.of(2016, 2, 7), "text"),
Day(LocalDate.of(2016, 2, 8), "text"),
Day(LocalDate.of(2016, 2, 9), "text"),
Day(LocalDate.of(2016, 2, 10), "text"),
Day(LocalDate.of(2016, 2, 11), "text"),
Day(LocalDate.of(2016, 2, 12), "text"),
Day(LocalDate.of(2016, 2, 13), "text"),
Day(LocalDate.of(2016, 2, 14), "text"),
Day(LocalDate.of(2016, 2, 15), "text"),
Day(LocalDate.of(2016, 2, 16), "text"),
Day(LocalDate.of(2016, 2, 17), "text")
)
// hard code, for example Tuesday
def groupDaysBy(list: Seq[Day]): List[List[Day]] = {
???
}
val result =
Seq(
Seq(Day(LocalDate.of(2016, 2, 1), "text")), // Separate
Seq(Day(LocalDate.of(2016, 2, 2), "text"), // Tuesday
Day(LocalDate.of(2016, 2, 3), "text"),
Day(LocalDate.of(2016, 2, 4), "text"),
Day(LocalDate.of(2016, 2, 5), "text"),
Day(LocalDate.of(2016, 2, 6), "text"),
Day(LocalDate.of(2016, 2, 7), "text"),
Day(LocalDate.of(2016, 2, 8), "text")),
Seq(Day(LocalDate.of(2016, 2, 9), "text"), // Tuesday
Day(LocalDate.of(2016, 2, 10), "text"),
Day(LocalDate.of(2016, 2, 11), "text"),
Day(LocalDate.of(2016, 2, 12), "text"),
Day(LocalDate.of(2016, 2, 13), "text"),
Day(LocalDate.of(2016, 2, 14), "text"),
Day(LocalDate.of(2016, 2, 15), "text")),
Seq(Day(LocalDate.of(2016, 2, 16), "text"), // Tuesday
Day(LocalDate.of(2016, 2, 17), "text"))
)
assert(groupDaysBy(list) == result)
I have a list of Day object, and I want to group every 7 days together and the start date can be any day (from Monday to Sunday, I give Tuesday as an example).
Above is the function and expected result for my requirement. I am wondering how can I take advantage of Scala collection API to achieve without tail recursive?

Answer 1

Here's what you can do:
// hard code, for example Tuesday
def groupDaysBy(list: Seq[Day]): Seq[Seq[Day]] = {
val (list1,list2)= list.span(_.date.getDayOfWeek != DayOfWeek.TUESDAY)
Seq(list1) ++ list2.grouped(7)
}
I would recommend taking day as a parameter instead of hardcoding though, so it becomes
// hard code, for example Tuesday
def groupDaysBy(list: Seq[Day], dayOfWeek: DayOfWeek): Seq[Seq[Day]] = {
val (list1,list2)= list.span(_.date.getDayOfWeek != dayOfWeek)
Seq(list1) ++ list2.grouped(7)
}
...
assert(groupDaysBy(list, DayOfWeek.TUESDAY) == result)

Answer 2

Map your list to create a Tuple(GroupKey, value) with GroupKey a value representing a uniq week (year*53 + week_of_the_year) for example. Then you can group on GroupKey