Inconsistent behaviour for xs.sliding(n) if n is less than size?

Question

According to scaladoc, sliding() returns... \"An iterator producing iterable collections of size size, except the last and the only element will be truncated if

Answer 1

It was a mistake, but wasn't fixed as of 2.9. Everyone occasionally makes design errors, and once one gets into the library it's a nontrivial task to remove it.

Workaround: add a filter.

xs.sliding(3).filter(_.size==3).toList

Answer 2

You can "work around" this by using the GroupedIterator#withPartial modifier.

scala> val xs = List(1, 2)
xs: List[Int] = List(1, 2)

scala> xs.iterator.sliding(3).withPartial(false).toList
res7: List[Seq[Int]] = List()

(I don't know why you need to say xs.iterator but xs.sliding(3).withPartial(false) does not work because you get an Iterator instead of a GroupedIterator.

Answer 3

EDIT:

Check Rex's answer (which is the correct one). I'm leaving this just because (as Rex said on the comments) it was the original (wrong) idea behind that design decision.

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I don't know why you would expect an empty list there, returning the full list seems like the best result, consider this example:

def slidingWindowsThing(windows : List[List[Int]]) { // do your thing

For this methods you probably want all these calls to work:

slidingWindowsThing((1 to 10).sliding(3))

slidingWindowsThing((1 to 3).sliding(3))

slidingWindowsThing((1 to 1).sliding(3))

This is why the method defaults to a list of size list.length instead of Nil (empty list).