Swift standard library already offers a useful set of sort() functions.
However, it is also often useful to know how the collection should be
rearranged in order to become sorted. For example, R defines the order()
function which returns a permutation of collection indexes which rearrange the
collection in an order. I suggest to add similar functionality to the Swift
Collections E.g.:
var out = []
for i in collection.order({$0 < $1}) { out.append(collection[i]) }
// out is now sorted collection
Knowing the sort order is useful in many applications where the data cannot or
should not be rearranged and yet some information about the ordering is
helpful, e.g. for traversing the collection in a specific way. It is also
helpful for maintaining multiple ordering relations associated with the same
collection.
The implementation should be fairly straightforward. E.g. here is an extension
method I use:
extension CollectionType {
func order(@noescape isOrderedBefore: (Self.Generator.Element,
Self.Generator.Element) -> Bool) -> [Self.Index] {
return indices.sort({ isOrderedBefore(self[$0], self[$1]) })
}
}
Best,
Taras
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