Question

In Scala I have a list of objects that represent points and contain x and y values. The list describes a path that goes through all these points sequentially. My question is how to use folding on that list in order to find the total length of the path? Or maybe there is even a better functional or Scala way to do this?

What I have came up with is this:

def distance = (0 /: wps)(Waypoint.distance(_, _)) 

but ofcourse this is totally wrong because distance returns Float, but accepts two Waypoint objects.

UPDATE:

Thanks for the proposed solutions! They are definitely interesting, but I think that this is too much functional for real-time calculations that may become heavy. So far I have came out with these lines:

val distances = for(i <- 0 until wps.size) yield wps(i).distanceTo(wps(i + 1))
val distance = (0f /: distances)(_ + _)

I feel this to be a fair imperative/functional mix that is both fast and also leaves the distances values between each waypoint for further possible references which is also a benifit in my case.

UPDATE 2: Actually, to determine, what is faster, I will have to do benchmarks of all the proposed solutions on all types of sequences.

Answer 1

This should work.

(wps, wps drop 1).zipped.map(Waypoint.distance).sum