How can I sort multiple arrays based on the sorted order of another array

Question

I have multiple arrays, and I want to sort all of them based on the sorted order of one of them, like so:

var myArr = ["b", "a", "c"]
var myArr2 = ["letter b", "letter a", "letter c"]
var myArr3 = ["b is the second letter", "a is the first letter", "c is the third letter"]
func sortMultipleArraysBasedOnOne(alphabeticallyArray:Array, arrays:[Array]){
 //order myArr alphabetically
 for array in arrays{
 //change all arrays indexes like in myArr
 }
}
sortMultipleArraysBasedOnOne(myArr, [myArr2, myArr3])

I expect after function execution the arrays will be like this:

myArr = ["a", "b", "c"]
myArr2 = ["letter a", "letter b", "letter c"]
myArr3 = ["a is the first letter", "b is the second letter", "c is the third letter"]

Answer 1

You can do this by first sorting an array of the keying array’s indices by the values they index, then generating new arrays based on those sorted indices, using PermutationGenerator:

let myArr = ["b", "a", "c"]
let myArr2 = ["letter b", "letter a", "letter c"]
let myArr3 = ["b is the second letter", "a is the first letter", "c is the third letter"]
func sortByKeyArray(keyArray: [String], valuesArrays: [[String]]) -> [[String]] {
 precondition(reduce(valuesArrays, true) { 0ドル.0 && (0ドル.1.count == keyArray.count)},
 "Arrays all need to be the same length")
 let permutation = sorted(indices(keyArray)) {
 keyArray[0ドル] < keyArray[1ドル]
 }
 return valuesArrays.map {
 Array(PermutationGenerator(elements: 0,ドル indices: permutation))
 }
}
sortByKeyArray(myArr, [myArr2, myArr3])
// returns [["letter a", "letter b", "letter c"], ["a is the first letter", "b is the second letter", "c is the third letter"]]

---

If you want to make this generic on any kind of collection (but still returning an array, in the same style as the std lib collection algos):

func sortByKeyingCollection<C: CollectionType, D: SequenceType 
 where D.Generator.Element == C, 
 C.Index: RandomAccessIndexType, 
 C.Generator.Element: Comparable>
(key: C, values: D) -> [[C.Generator.Element]] {
 let permutation = sorted(indices(key)) {
 key[0ドル] < key[1ドル]
 }
 return map(values) {
 Array(PermutationGenerator(elements: 0,ドル indices: permutation))
 }
}

And a version that takes a custom comparator:

func sortByKeyingCollection<C: CollectionType, D: SequenceType where D.Generator.Element == C, C.Index: RandomAccessIndexType>(key: C, values: D, isOrderedBefore: (C.Generator.Element,C.Generator.Element)->Bool) -> [[C.Generator.Element]] {
 let permutation = sorted(indices(key)) {
 isOrderedBefore(key[0ドル],key[1ドル])
 }
 return map(values) {
 Array(PermutationGenerator(elements: 0,ドル indices: permutation))
 }
}
sortByKeyingCollection(myArr, [myArr2, myArr3], >)
sortByKeyingCollection(myArr, [myArr2, myArr3], lexicographicalCompare)
sortByKeyingCollection(myArr, [myArr2, myArr3]) { dropFirst(0ドル) < dropFirst(1ドル) }

• Bogdan Bogdanov: can you edit it for Swift 2.1 with Int example 1,2,3 ?

Answer 2

From what I understand, you want to order your array alphabetically. If so, you can use one of the example below :

Example 1

var anArray1 = ["b","a","d","e","c"]
func alphabeticallyOrder(lt : String, rt: String) -> Bool {
 return lt < rt
}
anArray1 = sorted(anArray1, alphabeticallyOrder)
println(anArray1) // [a, b, c, d, e]

Example 2

var anArray2 = ["b","a","d","e","c"]
anArray2 = sorted(anArray2, {0ドル < 1ドル})
println(anArray2) // [a, b, c, d, e]

Example 3

var anArray3 = ["b","a","d","e","c"]
anArray3 = sorted (anArray3 , <)
println(anArray3) // [a, b, c, d, e]

Edit : My bad, you also want to change the other arrays indexes in the process. I'll edit later if required.