Count consecutive occurrences in List[List[]]

Question

I have a List of Lists, in which I need to count the consecutive occurrences of a given element.

The list is structured as follows:

List[List[Attendance]]

Attendance(val scheduleId: Long,
           val date: LocalDate,
           val teamId: Long,
           val memberId: Long,
           var attendance: AttendanceType)

I need to check the number of times a given element in the list has AttendanceType == In is followed by the same AttendanceType == In.

I have seen people use containsSlice() and Seq(x, y) for checking that this occurs once, but not counting the number of times it happens.

Answer 1

Something like this?

def countSeqDup(l: List[List[Attendance]], in: AttendanceType): Int =
  l.flatten.sliding(2).count{ x => x(0).attendance == in && x(1).attendance == in}

The flatten creates a single list of values and sliding groups them in adjacent pairs, so then it is just a question of counting pairs that match.

Note that this will fail if there are fewer than 2 elements in total.