Here are 2 arrays: countriesVotedKeys and dictionnaryCountriesVotes.
I need to build a dictionary, whose keys are all the items from countriesVotedKeys, and its values are all the items from dictionnaryCountriesVotes. Both arrays contains same number of elements.
I've tried many things, but none lead to desired result.
for value in self.countriesVotedValues! {
for key in self.countriesVotedKeys! {
self.dictionnaryCountriesVotes![key] = value
}
}
I can clearly see why this code produce bad result: second array is iterated in its entirity at each iteration of first array. I also tried a classical for var i= 0, var j= 0;...... but it seems this kind of syntax is not allowed in swift.
In short, i'm stuck. Again.
Swift 4
let keys = ["key1", "key2", "key3"]
let values = [100, 200, 300]
let dict = Dictionary(uniqueKeysWithValues: zip(keys, values))
print(dict) // "[key1: 100, key3: 300, key2: 200]"
Swift 3
var dict: [String: Int] = [:]
for i in 0..<keys.count {
dict[keys[i]] = values[i]
}
Use NSDictionary's convenience initializer:
let keys = ["a", "b", "c"]
let values = [1,2,3]
var dict = NSDictionary(objects: values, forKeys: keys) as [String: Int]
Related
I have a dictionary with this structure:
a: [1,2]
b: [3,4]
c: [5,6]
and I need to return a string with this structure.
a,b,c\n1,3,5\n2,4,6
I solved the first part of the string. But to get the rest of the String. I try to iterate into my dictionary to get the first elements for each key in my dictionary and then get the rest for each value into the array.
Is there an easier way to get this?
Once you know what's the order of the keys (alpha ?), you can use this:
let dict: [String: [Int]] = ["a": [1,2], "b": [3, 4], "c": [5, 6]]
let keys = dict.keys.sorted() //Or do whatever you want here to get your target order
var matrix: [[String]] = []
keys.forEach {
guard let arrayAsInt = dict[$0] else { return }
let arrayAsString = arrayAsInt.map{ "\($0)" }
matrix.append( [$0] + arrayAsString)
}
print("Matrix: \(matrix)")
let transposed = matrix.transposed()
print("Transposed Matrix: \(transposed)")
let output = transposed.map { $0.joined(separator: ",")}.joined(separator: "\n")
print(output)
The outputs:
$>Matrix: [["a", "1", "2"], ["b", "3", "4"], ["c", "5", "6"]]
$>Transposed Matrix: [["a", "b", "c"], ["1", "3", "5"], ["2", "4", "6"]]
$>a,b,c
1,3,5
2,4,6
Obvisouly the "\n" might be invisible and be an actual new line
a,b,c
1,3,5
2,4,6
Being
a,b,c\n1,3,5\n2,4,6
What's the idea behind that? Create a matrix and use the transpose (it's used in maths with matrix, it's one of the basic modification of a matrix).
First transform the [String: [Int]] into a [[String]], where each element would be key followed by its values. I transformed it there as String for simpler code later.
Why doing that? Because the matrix value is easy to get from your initial dict. the transposed value is harder (not impossible) to get from dict but easier from matrix, and the transposed is quickly transformed into your format.
So my thinking was the reverse:
Get a structure from your output, then how to get it, it's a transpose, so I need to get the initial input as it, etc.
With the help of a code for Transpose Matrix (that accept String elements).
extension Collection where Self.Iterator.Element: RandomAccessCollection {
// PRECONDITION: `self` must be rectangular, i.e. every row has equal size.
func transposed() -> [[Self.Iterator.Element.Iterator.Element]] {
guard let firstRow = self.first else { return [] }
return firstRow.indices.map { index in
self.map{ $0[index] }
}
}
}
Any code (there a various) working ones, should the trick. I took it from here.
As pointed by #Leo Dabus, you can remove the Self.Iterator.Element
from the extension code (twice). I just wanted to it as such, not modifying the initial answer since it's not mind.
What you are looking for, besides composing the final string, is how to transpose a collection (this would work with collections of different sizes as well):
extension Sequence {
func max<T: Comparable>(_ predicate: (Element) -> T) -> Element? {
self.max(by: { predicate($0) < predicate($1) })
}
}
extension Collection where Element: RandomAccessCollection, Element.Indices == Range<Int> {
func transposed() -> [[Element.Element]] {
(0..<(max(\.count)?.count ?? .zero)).map {
index in compactMap { $0.indices ~= index ? $0[index] : nil }
}
}
}
let dict = ["a": [1,2,3],
"b": [4,5,6],
"c": [7,8,9]]
let sorted = dict.sorted(by: {$0.key < $1.key})
let result = sorted.map(\.key).joined(separator: ",") + "\n" +
sorted.map(\.value).transposed().map {
$0.map(String.init).joined(separator: ",")
}.joined(separator: "\n")
result // "a,b,c\n1,4,7\n2,5,8\n3,6,9"
A dictionary is an unordered collection so you need to sort it according to any specific key. Here I sort the dictionary according to the key if you don't care about an order you can just remove sort.
let dict: [String: Any] = ["a": [1,2], "b": [3,4], "c": [5,6]]
let sortedKey = dict.keys.sorted(by: <)
let key = sortedKey.joined(separator: ",")
var firstValues: [String] = []
var secondValues: [String] = []
sortedKey.forEach { (key) in
if let dictValue = dict[key] as? [Int],
let firstValue = dictValue.first,
let secondValue = dictValue.last {
firstValues.append("\(firstValue)")
secondValues.append("\(secondValue)")
}
}
let finalString = key + "\n" + firstValues.joined(separator: ",") + "\n" + secondValues.joined(separator: ",")
print(finalString) // "a,b,c\n1,3,5\n2,4,6"
I'm trying to figure out the best way in Swift to add values to an Array that is a Value in a Dictionary. I want to build a dictionary of contacts sorted by the first letter of their first name. For example [A : [Aaron, Adam, etc...], B : [Brian, Brittany, ect...], ...]
I found this function:
updateValue(_:forKey:)
And tried using it in a loop:
for contact in self.contacts.sorted() {
self.contactDictionary.updateValue([contact], forKey: String(describing: contact.characters.first))
}
But when I tried to use that it replaced the existing array with a new one. I know I can manually check to see if the key in the dictionary exists, if it does, retrieve the array and then append a new value, otherwise add the new key/value pair but I'm not sure if Swift provides an easier/better way to do this.
Any insight would be much appreciated!
You can use reduce(into:) method (Swift4) and as follow:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
// make sure there is at least one letter in your string else return
guard let first = element.first else { return }
// create a string with that initial
let initial = String(first)
// initialize an array with one element or add another element to the existing value
result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
If you are using Swift3 or earlier you would need to create a mutable result dictionary inside the closure:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce([String:[String]]()) { result, element in
var result = result
guard let first = element.first else { return result }
let initial = String(first)
result[initial] = (result[initial] ?? []) + [element]
return result
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
Note that the result is not sorted. A dictionary is an unordered collection. If you need to sort your dictionary and return an array of (key, Value) tuples you can use sorted by key as follow:
let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)
"[(key: "A", value: ["Aaron", "Adam"]), (key: "B", value: ["Brian", "Brittany"])]\n"
Swift 4's new dictionary initializers can do it all for you:
let contactInitials = contacts.filter{!$0.isEmpty}.map{ ($0.first!,[$0]) }
let dict = [Character:[String]](contactInitials, uniquingKeysWith:+)
I'm trying to figure out the best way in Swift to add values to an Array that is a Value in a Dictionary. I want to build a dictionary of contacts sorted by the first letter of their first name. For example [A : [Aaron, Adam, etc...], B : [Brian, Brittany, ect...], ...]
I found this function:
updateValue(_:forKey:)
And tried using it in a loop:
for contact in self.contacts.sorted() {
self.contactDictionary.updateValue([contact], forKey: String(describing: contact.characters.first))
}
But when I tried to use that it replaced the existing array with a new one. I know I can manually check to see if the key in the dictionary exists, if it does, retrieve the array and then append a new value, otherwise add the new key/value pair but I'm not sure if Swift provides an easier/better way to do this.
Any insight would be much appreciated!
You can use reduce(into:) method (Swift4) and as follow:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
// make sure there is at least one letter in your string else return
guard let first = element.first else { return }
// create a string with that initial
let initial = String(first)
// initialize an array with one element or add another element to the existing value
result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
If you are using Swift3 or earlier you would need to create a mutable result dictionary inside the closure:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce([String:[String]]()) { result, element in
var result = result
guard let first = element.first else { return result }
let initial = String(first)
result[initial] = (result[initial] ?? []) + [element]
return result
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
Note that the result is not sorted. A dictionary is an unordered collection. If you need to sort your dictionary and return an array of (key, Value) tuples you can use sorted by key as follow:
let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)
"[(key: "A", value: ["Aaron", "Adam"]), (key: "B", value: ["Brian", "Brittany"])]\n"
Swift 4's new dictionary initializers can do it all for you:
let contactInitials = contacts.filter{!$0.isEmpty}.map{ ($0.first!,[$0]) }
let dict = [Character:[String]](contactInitials, uniquingKeysWith:+)
My dictionary like this:
var items = [Int: [String]]()
var itemsResult = [Int: [String]]()
itmesResult stores the data downloaded from server.
and pass the data to items use of items = itmesResult
the value has 3 elements like ["Apple","/image/apple.png","29"]
and I want to sort the dictionary by first value which is Apple.
for (k,v) in (itemsResult.sorted(by: { $0.value[0] < $1.value[0] })) {
items[k] = v
}
The result of above code is not my expectation.
I would like to sort it alphabetically how can I do this?
Edit:
origin:
1:["Apple","/image/apple.png","29"]
2:["AAA","/image/aaa.png","29"]
3:["Banana","/image/banana.png","29"]
sorted:
2:["AAA","/image/aaa.png","29"]
1:["Apple","/image/apple.png","29"]
3:["Banana","/image/banana.png","29"]
I would like to sort it by first value.
So if I take your example, this does the trick:
var items = [Int: [String]]()
items[0] = ["Apple","/image/apple.png","29"]
items[1] = ["AAA","/image/aaa.png","29"]
items[2] = ["Banana","/image/banana.png","29"]
let itemResult = items.sorted { (first: (key: Int, value: [String]), second: (key: Int, value: [String])) -> Bool in
return first.value.first! < second.value.first!
}
print (itemResult)
The right thing to do is to use objects of course, and note that I'm not null checking the "first" object in each array, but this is not a problem to change.
Let me know if this is what you were looking for, the output is:
[(1, ["AAA", "/image/aaa.png", "29"]), (0, ["Apple", "/image/apple.png", "29"]), (2, ["Banana", "/image/banana.png", "29"])]
EDIT:
Also note, that this case doesn't actually "sort" the dictionary, because a dictionary is by definition not sorted, this creates an array of key-value objects sorted using the array indexes
Instead of saving these variable into an array of arrays, make them an array of dictionaries.
You can do this like so:
var dictionaries:[Dictionary<String, String>] = []
for item in items {
let dictionary = {"name": item[0], "url": item[1], "id" : item[2]}
dictionaries.append(dictionary)
}
You can get your sorted list of dictionaries like this:
dictionaries.sorted(by: { $0["name"] < $1["name"] })
I know there is a new shuffle method with iOS 9
but I am wondering if there is anyway to shuffle two arrays the same way?
For example
[1,2,3,4] and [a,b,c,d]
shuffle
[3,4,1,2] and [c,d,a,b]
Using the shuffle() method from How do I shuffle an array in Swift? and the ideas from How can I sort multiple arrays based on the sorted order of another array
you can shuffle the array indices and then re-order both (or more)
arrays accordingly:
let a = [1, 2, 3, 4]
let b = ["a", "b", "c", "d"]
var shuffled_indices = a.indices.shuffle()
let shuffled_a = Array(PermutationGenerator(elements: a, indices: shuffled_indices))
let shuffled_b = Array(PermutationGenerator(elements: b, indices: shuffled_indices))
print(shuffled_a) // [3, 1, 2, 4]
print(shuffled_b) // ["c", "a", "b", "d"]
Update for Swift 3 (Xcode 8): PermutationGenerator does not
exist in Swift 3 anymore.
Using the shuffled() method
from Shuffle array swift 3 the same can be achieved with
var shuffled_indices = a.indices.shuffled()
let shuffled_a = shuffled_indices.map { a[$0] }
let shuffled_b = shuffled_indices.map { b[$0] }
Use a dictionary to store the values temporarily, shuffle the keys and then rebuild the other array by extracting the values from the dictionary.
I'm unaware of any built-in shuffle mechanism in Swift 2.0. Assuming this doesn't exist, I borrowed some code from here.
extension CollectionType where Index == Int {
/// Return a copy of `self` with its elements shuffled
func shuffle() -> [Generator.Element] {
var list = Array(self)
list.shuffleInPlace()
return list
}
}
extension MutableCollectionType where Index == Int {
/// Shuffle the elements of `self` in-place.
mutating func shuffleInPlace() {
// empty and single-element collections don't shuffle
if count < 2 { return }
for i in 0..<count - 1 {
let j = Int(arc4random_uniform(UInt32(count - i))) + i
guard i != j else { continue }
swap(&self[i], &self[j])
}
}
}
let shuffleOrder = [0,1,2,3]
let shuffled = shuffleOrder.shuffle()
var newArray1 = [String]()
var newArray2 = [String]()
let array1 = ["a", "b", "c", "d"]
let array2 = ["w", "x", "y", "z"]
shuffled.forEach() { index in
newArray1.append(array1[index])
newArray2.append(array2[index])
}
This solves the problem in a really straight forward way. It creates an array, shuffleOrder, that just has an index for each possible index in the starting arrays. It then shuffles these indices to create a random sampling order. Finally, it constructs two new arrays, based off of the starting arrays, sampling them with the shuffled values. While this doesn't mutate the original 2 arrays in place, it would be simple to modify this to do so.
Based upon Martin R's original answer, you could approach the problem using GameKit.
The answer is written in Swift4:
var arrayA = [1, 2, 3, 4]
var arrayB = ["a", "b", "c", "d"]
//Get The Indices Of The 1st Array
var shuffledIndices: [Int] = Array(arrayA.indices)
print("Shuffled Indices = \(shuffledIndices)")
//Shuffle These Using GameKit
shuffledIndices = GKRandomSource.sharedRandom().arrayByShufflingObjects(in: shuffledIndices) as! [Int]
//Map The Objects To The Shuffled Indices
arrayA = shuffledIndices.map { arrayA[$0] }
arrayB = shuffledIndices.map { arrayB[$0] }
//Log The Results
print("""
Array A = \(arrayA)
Array B = \(arrayB)
""")
Hope it helps ^_________^.