Turn Together With Confront The Strange: Using A C Component Division To Merge (Or Stable) Assort Inward Swift (Swift 3, Xcode 8)
It was suggested that Swift include a stable (or merge) kind business office together with I promise this becomes the case. At present, however, nosotros must plow to pure Swift implementations presented past times others or plow to the C functions accessible through Swift. (According to the man pages, mergesort: is a stable kind function.)
It should last noted that the mergesort: function has to a greater extent than or less restrictions that brand generic work hard if non impossible. Not to the lowest degree connected to closures, but at the 2nd I only desire to hold off at the basics of mergesort:
public func mergesort(_ __base: UnsafeMutableRawPointer!, _ __nel: Int, _ __width: Int, _ __compar: @escaping @convention(c) (UnsafeRawPointer?, UnsafeRawPointer?) -> Int32) -> Int32This is quite an unwieldy looking business office but let's pause it down.
- base: this is a pointer to a mutable array, which tin dismiss last implemented using the in-out notation of & so &arrayName is what you'll run across here
- nel: is the array length, therefore arrayName.count goes here
- width: is the byte width of the values contained inward the array, therefore hither nosotros insert for illustration MemoryLayout<Int>.size where betwixt the angle brackets goes the type
- compar: is where nosotros work a closure to create upwards one's hear how the kind volition create got house together with the values come upwards via UnsafeRawPointers. To larn at the value pointed to past times the pointers together with brand the comparing y'all tin dismiss work something similar this, $0.unsafelyUnwrapped.load(as: Int.self) > $1.unsafelyUnwrapped.load(as: Int.self). As I empathise it here nosotros must provide an Int32 together with are instructing through this integer how far the index should last advanced. So if nosotros create got a comparing betwixt 2 values, equally nosotros when the array is iterated over inward the sort, together with those 2 values are equal in that location should last no advancement inward the (first) value beingness compared but if the value is less than the 2nd value it moves backwards (or rather stays to the left of the 2nd value) together with if the value is greater than the 2nd value therefore it moves frontwards past times 1 (moving past times the 2nd value). And this comparing keeps happening until the array is sorted.
var array = ["mango", "apple", "pear", "orange", "banana"] mergesort(&array, array.count, MemoryLayout<String>.size, { allow a = $0.unsafelyUnwrapped.load(as:String.self) allow b = $1.unsafelyUnwrapped.load(as:String.self) if a == b { provide 0 } else if a < b { provide -1 } else { provide 1 } }) print(array) // ["apple", "banana", "mango", "orange", "pear"]
Further fun
I idea it worth implementing secondary sorting to extend the practise together with these are my firstly steps here:
enum SortType { instance Ascending instance Descending } enum SortError:Error { instance ArrayLengthsNotEqual } enum SortBy { instance IntegerArray([Int], type:SortType), DoubleArray([Double], type:SortType), StringArray([String], type:SortType) init?<S: Sequence>(arr: S, type:SortType = .Ascending) { if arr is [Int] { self = SortBy.IntegerArray(arr as! [Int], type: type) } else if arr is [Double] { self = SortBy.DoubleArray(arr as! [Double], type: type) } else if arr is [String] { self = SortBy.StringArray(arr as! [String], type: type) } else { provide zero } } func sort<A>(arr:Array<A>) throws -> Array<A> { switch self { instance .IntegerArray(let i): guard i.0.count == arr.count else {throw SortError.ArrayLengthsNotEqual} var arr = zip(i.0,arr).flatMap{$0} if i.type == .Ascending { mergesort(&arr, arr.count, MemoryLayout<(Int,A)>.size, { allow a = $0.unsafelyUnwrapped.load(as:(Int.self, Any.self).0) allow b = $1.unsafelyUnwrapped.load(as:(Int.self, Any.self).0) if a == b {return 0} else if a < b {return -1} else { provide 1 } } ) } else { mergesort(&arr, arr.count, MemoryLayout<(Int,A)>.size, { allow a = $0.unsafelyUnwrapped.load(as:(Int.self, Any.self).0) allow b = $1.unsafelyUnwrapped.load(as:(Int.self, Any.self).0) if a == b { provide 0 } else if a > b { provide -1 } else { provide 1 } } ) } provide arr.map{$0.1} instance .DoubleArray(let d): guard d.0.count == arr.count else {throw SortError.ArrayLengthsNotEqual} var arr = zip(d.0,arr).flatMap{$0} if d.type == .Ascending { mergesort(&arr, arr.count, MemoryLayout<(Double,A)>.size, { allow a = $0.unsafelyUnwrapped.load(as:(Double.self, Any.self).0) allow b = $1.unsafelyUnwrapped.load(as:(Double.self, Any.self).0) if a == b {return 0} else if a < b {return -1} else {return 1}}) } else { mergesort(&arr, arr.count, MemoryLayout<(Double,A)>.size, { allow a = $0.unsafelyUnwrapped.load(as:(Double.self, Any.self).0) allow b = $1.unsafelyUnwrapped.load(as:(Double.self, Any.self).0) if a == b {return 0} else if a > b {return -1} else {return 1}}) } provide arr.map{$0.1} instance .StringArray(let str): guard str.0.count == arr.count else {throw SortError.ArrayLengthsNotEqual} var arr = zip(str.0,arr).flatMap{$0} if str.type == .Ascending { mergesort(&arr, arr.count, MemoryLayout<(String,A)>.size, { allow a = $0.unsafelyUnwrapped.load(as:(String.self, Any.self).0) allow b = $1.unsafelyUnwrapped.load(as:(String.self, Any.self).0) if a == b {return 0} else if a < b {return -1} else {return 1}}) } else { mergesort(&arr, arr.count, MemoryLayout<(String,A)>.size, { allow a = $0.unsafelyUnwrapped.load(as:(String.self, Any.self).0) allow b = $1.unsafelyUnwrapped.load(as:(String.self, Any.self).0) if a == b {return 0} else if a > b {return -1} else {return 1}}) } provide arr.map{$0.1} }} } And implementation looks similar this: // information var arr1 = ["3892", "3926", "3977", "4028", "4030", "4043", "4059", "4062", "2547", "2622", "2691", "3913"].map{Double($0)!} var arr2 = ["A", "K", "L", "B", "M", "N", "O", "P", "Q", "T", "S", "V"] var arr3 = [1, 2, 4, 1, 9, 10, 8, 9, 11, 12, 14, 13] arr3 // implementatation // firstly create your sorter, the ordering array (used to create the SortBy instance) must comprise Int, Double, or String if allow sorter = SortBy(arr: arr3) { produce { arr1 = endeavour sorter.sort(arr: arr1) arr2 = endeavour sorter.sort(arr: arr2) arr3 = endeavour sorter.sort(arr: arr3) } grab SortError.ArrayLengthsNotEqual { print("Array lengths are non equal, no sorting has taken place!!!") } grab { print("other error, no sorting has taken place!!!") } } arr3 //[1, 1, 2, 4, 8, 9, 9, 10, 11, 12, 13, 14] arr2 // ["A", "B", "K", "L", "O", "M", "P", "N", "Q", "T", "V", "S"] arr1 // [4028, 3892, 3926, 3977, 4059, 4062, 4030, 4043, 2547, 2622, 3913, 2691] I require to seek this code together with brand certain it industrial plant consistently but it seems to be. (As I noted at the start the lack of generics when using C functions throttle things a little.)
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