I might have an array that looks like the following:
[1, 4, 2, 2, 6, 24, 15, 2, 60, 15, 6]
Or, reall
Here's a category on SequenceType
which preserves the original order of the array, but uses a Set
to do the contains
lookups to avoid the O(n)
cost on Array's contains(_:)
method.
public extension Sequence where Element: Hashable {
/// Return the sequence with all duplicates removed.
///
/// i.e. `[ 1, 2, 3, 1, 2 ].uniqued() == [ 1, 2, 3 ]`
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234, as
/// per @Alexander's comment.
func uniqued() -> [Element] {
var seen = Set()
return self.filter { seen.insert($0).inserted }
}
}
If you aren't Hashable or Equatable, you can pass in a predicate to do the equality check:
extension Sequence {
/// Return the sequence with all duplicates removed.
///
/// Duplicate, in this case, is defined as returning `true` from `comparator`.
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
func uniqued(comparator: @escaping (Element, Element) throws -> Bool) rethrows -> [Element] {
var buffer: [Element] = []
for element in self {
// If element is already in buffer, skip to the next element
if try buffer.contains(where: { try comparator(element, $0) }) {
continue
}
buffer.append(element)
}
return buffer
}
}
Now, if you don't have Hashable, but are Equatable, you can use this method:
extension Sequence where Element: Equatable {
/// Return the sequence with all duplicates removed.
///
/// i.e. `[ 1, 2, 3, 1, 2 ].uniqued() == [ 1, 2, 3 ]`
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
func uniqued() -> [Element] {
return self.uniqued(comparator: ==)
}
}
Finally, you can add a key path version of uniqued like this:
extension Sequence {
/// Returns the sequence with duplicate elements removed, performing the comparison usinig the property at
/// the supplied keypath.
///
/// i.e.
///
/// ```
/// [
/// MyStruct(value: "Hello"),
/// MyStruct(value: "Hello"),
/// MyStruct(value: "World")
/// ].uniqued(\.value)
/// ```
/// would result in
///
/// ```
/// [
/// MyStruct(value: "Hello"),
/// MyStruct(value: "World")
/// ]
/// ```
///
/// - note: Taken from stackoverflow.com/a/46354989/3141234
///
func uniqued(_ keyPath: KeyPath) -> [Element] {
self.uniqued { $0[keyPath: keyPath] == $1[keyPath: keyPath] }
}
}
You can stick both of these into your app, Swift will choose the right one depending on your sequence's Iterator.Element
type.