on Mon Apr 11 2016, Taras Zakharko <[email protected]> wrote:
> Hi,
>
> I think it depends on how expensive the indexed access is on the collection. I
> use it primarily on arrays, where self[i] essentially boils down to a pointer
> dereference, so I expect the generated code to be very efficient. Your version
> might be faster for collection with expensive element access, but it should be
> slower for arrays and the like, as it involves additional intermediate
> structure
> allocations and copies.
>
> — Taras
>
> Just a side note that you could also:
>
> extension SequenceType {
> func order(@noescape isOrderedBefore: (Generator.Element,
> Generator.Element)
> -> Bool) -> [Int] {
> return enumerate().sort{ isOrderedBefore($0.1, $1.1) }.map{ $0.0 }
> }
> }
>
> (0...3).reverse().order(<) // [3, 2, 1, 0]
>
> This way you can `order` all sequences, and it is more efficient as you
> don’t fetch elements by index inside the `isOrderedBefore`. (You could
> also
> *not* `map` at the end and return all the elements along with their
> original
> indexes.)
>
This is about as efficient as it gets:
extension CollectionType {
func order(@noescape isOrderedBefore areInOrder: (Generator.Element,
Generator.Element) -> Bool) -> [Index] {
var a = Array(indices)
a.sortInPlace { areInOrder(self[$0], self[$1]) }
return a
}
}
--
Dave
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