Scala列表按日期差异过滤

Question

I've got a problem and I don't really know how to do it in a proper Scala way.

I've got a list of objects, holding a date. I want to do something like this:

I want to make a selection using an acceptable time value, like 2 hours, between 2 successors in the list. The purpose is to keeps user trend comparing to a point (if he shows up 2 times here, or 1 or 15 !).

The algorithm I imagined:

• Let's keep 2 points A and B. We calculate the time difference between the 2 points and then evaluate if it's acceptable or not (>2h, acceptable).
• If it's not acceptable, we reject B and then new B is the next list element.
• If acceptable, B becomes A and the new B is the next list element.

How to do it, with some filters or collects? Oh and if the algorithm doesn't sounds good for you, I'm open to criticism!

Edit: I'm not asking for the solution, but just the right functions to lookup!

Answer 1

Say I have a list of integers, and I want to step through them and only keep the ones which are more than 1 greater than the previous. I would use foldLeft to step through them, building a list of only the items which are acceptable:

val nums = List(1,2,4,5,7)

nums.foldLeft(List[Int]()){
  case (List(), b) => List(b)
  case (list, b) if b - list.head > 1 =>  list :+ b
  case (list, b) => list
}