Related
"Is it possible to remove for .. in (to make it more Swifty) ?
let arr1 = ["Bill", "John", "Richard", "Donald", "George"]
let arr2 = ["ill", "ck", "rd", "ld"]
var arr3 = Array<String>()
for str in arr2
{
arr3 += arr1.filter{ $0.hasSuffix(str) }
}
debugPrint(arr3) // ["Bill", "Richard", "Donald"]
Thank you !
Yes it is. Use the map function in conjunction with flatMap. If you want no doubled (e. g. when suffix is "d"), use Set():
let names = ["Bill", "John", "Richard", "Donald", "George"]
let suffixes = ["ill", "ck", "rd", "ld", "d"]
let namesWithSuffixes = Set(suffixes.map({ suffix in names.filter({ name in name.hasSuffix(suffix) }) }).flatMap({ $0 }))
But if you just want to get rid of the old for loop, you can use forEach():
var arr3 = [String]()
suffixes.forEach({ suffix in
arr3 += names.filter({ $0.hasSuffix(suffix) })
})
Be aware that your original solution and the second one only causes 24 executions while the "swifty" map.filter.flatmap uses 29 executions.
Wouldn't this be more concise and straightforward ?
arr3 = arr1.filter{name in arr2.contains{name.hasSuffix($0)}}
I have a collection view made up of 4 sections.
Each section is an array of strings, like this:
var picList: [String] = ["Bird", "Cat", "Cow", "Dog", "Duck", "Elephant", "Fish", "Giraffe", "Lion", "Mouse", "Sheep", "Snake" ]
var vehiclesList: [String] = ["Airplane", "Ambulance", "Boat", "Bus", "Car", "Fire_Engine", "Helicopter", "Motorcycle", "Tank", "Tractor", "Train", "Truck" ]
var fruitsList: [String] = ["Apple", "Banana", "Grapes", "Mango", "Orange", "Peach", "Pineapple", "Strawberry", "Watermelon" ]
var bodyPartsList: [String] = ["Arm", "Ear", "Eye", "Face", "Feet", "Hand", "Hair", "Legs", "Mouth", "Nose" ]
I created a UITapGestureRecognizer for the cell, that when I click on the cell, I get the index.
Here is the tapMethod
func handleTap(sender: UITapGestureRecognizer) {
print("tap")
if let indexPath = self.collectionView?.indexPathForItem(at: sender.location(in: self.collectionView)) {
let cell = collectionView?.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! PicViewCell
print("index path: + \(indexPath)")
} else {
print("")
}
}
Now the index prints like this [0,0] (if I press on the first item, ie bird). [2,4] if I press on the 4th item in the 2nd secion (ie mango). But I don't know how to translate the index, to get the corresponding string value. I mean something like this:
var itemName: String = [2,4] (and itemName would be mango)
I'm new to swift, so any help would be great.
Thanks so much.
What you need is an array of arrays, aka a 2D array - [[String]].
var array = [picList, vehicleList, fruitsList, bodyPartsList]
Then, you can access this with 2 indices like this:
var itemName = array[2][4]
You can create a two dimensional array, and add there your lists, indexpath.section will be the index of list and indexpath.item will be the index in thst list
I have a large array and need to access it by a key (a lookup) so I need to create Dictionary. Is there a built in function in Swift 3.0 to do so, or do I need to write it myself?
First I will need it for a class with key "String" and later on maybe I will be able to write a template version for general purpose (all types of data and key).
Note for 2019. This is now simply built-in to Swift 5, uniqueKeysWithValues and similar calls.
Is that it (in Swift 4)?
let dict = Dictionary(uniqueKeysWithValues: array.map{ ($0.key, $0) })
Note:
As mentioned in the comment, using uniqueKeysWithValues would give a fatal error (Fatal error: Duplicate values for key: 'your_key':) if you have duplicated keys.
If you fear that may be your case, then you can use init(_:uniquingKeysWith:) e.g.
let pairsWithDuplicateKeys = [("a", 1), ("b", 2), ("a", 3), ("b", 4)] // or `let pairsWithDuplicateKeys = array.map{ ($0.key, $0) }`
let firstValues = Dictionary(pairsWithDuplicateKeys, uniquingKeysWith: { (first, _) in first })
print(firstValues)
//prints ["a": 1, "b": 2]
let lastValues = Dictionary(pairsWithDuplicateKeys, uniquingKeysWith: { (_, last) in last })
print(lastValues)
//prints ["a": 3, "b": 4]
On Swift 4, you can achieve this by using Dictionary's grouping:by: initializer
For ex:
You have class named A
class A {
var name: String
init(name: String) {
self.name = name
}
// .
// .
// .
// other declations and implementions
}
Next, you have an array of objects of type A
let a1 = A(name: "Joy")
let a2 = A(name: "Ben")
let a3 = A(name: "Boy")
let a4 = A(name: "Toy")
let a5 = A(name: "Tim")
let array = [a1, a2, a3, a4, a5]
Let's say you want to create a Dictionary by grouping all the names by their first letter. You use Swifts Dictionary(grouping:by:) to achieve this
let dictionary = Dictionary(grouping: array, by: { $0.name.first! })
// this will give you a dictionary
// ["J": [a1], "B": [a2, a3], "T": [a4, a5]]
source
Note however that the resulting Dictionary "dictionary" is of type
[String : [A]]
it is not of type
[String : A]
as you may expect. (Use #uniqueKeysWithValues to achieve the latter.)
I think you're looking for something like this:
extension Array {
public func toDictionary<Key: Hashable>(with selectKey: (Element) -> Key) -> [Key:Element] {
var dict = [Key:Element]()
for element in self {
dict[selectKey(element)] = element
}
return dict
}
}
You can now do:
struct Person {
var name: String
var surname: String
var identifier: String
}
let arr = [Person(name: "John", surname: "Doe", identifier: "JOD"),
Person(name: "Jane", surname: "Doe", identifier: "JAD")]
let dict = arr.toDictionary { $0.identifier }
print(dict) // Result: ["JAD": Person(name: "Jane", surname: "Doe", identifier: "JAD"), "JOD": Person(name: "John", surname: "Doe", identifier: "JOD")]
If you'd like your code to be more general, you could even add this extension on Sequence instead of Array:
extension Sequence {
public func toDictionary<Key: Hashable>(with selectKey: (Iterator.Element) -> Key) -> [Key:Iterator.Element] {
var dict: [Key:Iterator.Element] = [:]
for element in self {
dict[selectKey(element)] = element
}
return dict
}
}
Do note, that this causes the Sequence to be iterated over and could have side effects in some cases.
As others already said, we need to understand which are the keys.
However I am trying to provide a solution to my interpretation of your question.
struct User {
let id: String
let firstName: String
let lastName: String
}
Here I am assuming that 2 users with the same id cannot exist
let users: [User] = ...
let dict = users.reduce([String:User]()) { (result, user) -> [String:User] in
var result = result
result[user.id] = user
return result
}
Now dict is a dictionary where the key is the user id and the value is the user value.
To access a user via its id you can now simply write
let user = dict["123"]
Update #1: General approach
Given an array of a given type Element, and a closure that determine the key of an Element, the following generic function will generate a Dictionary of type [Key:Element]
func createIndex<Key, Element>(elms:[Element], extractKey:(Element) -> Key) -> [Key:Element] where Key : Hashable {
return elms.reduce([Key:Element]()) { (dict, elm) -> [Key:Element] in
var dict = dict
dict[extractKey(elm)] = elm
return dict
}
}
Example
let users: [User] = [
User(id: "a0", firstName: "a1", lastName: "a2"),
User(id: "b0", firstName: "b1", lastName: "b2"),
User(id: "c0", firstName: "c1", lastName: "c2")
]
let dict = createIndex(elms: users) { $0.id }
// ["b0": {id "b0", firstName "b1", lastName "b2"}, "c0": {id "c0", firstName "c1", lastName "c2"}, "a0": {id "a0", firstName "a1", lastName "a2"}]
Update #2
As noted by Martin R the reduce will create a new dictionary for each iteration of the related closure. This could lead to huge memory consumption.
Here's another version of the createIndex function where the space requirement is O(n) where n is the length of elms.
func createIndex<Key, Element>(elms:[Element], extractKey:(Element) -> Key) -> [Key:Element] where Key : Hashable {
var dict = [Key:Element]()
for elm in elms {
dict[extractKey(elm)] = elm
}
return dict
}
let pills = ["12", "34", "45", "67"]
let kk = Dictionary(uniqueKeysWithValues: pills.map{ ($0, "number") })
["12": "number", "67": "number", "34": "number", "45": "number"]
swift5 swift4
The following converts an array to a dictionary.
let firstArray = [2,3,4,5,5]
let dict = Dictionary(firstArray.map { ($0, 1) } , uniquingKeysWith: +)
Swift 5
extension Array {
func toDictionary() -> [Int: Element] {
self.enumerated().reduce(into: [Int: Element]()) { $0[$1.offset] = $1.element }
}
}
This extension works for all sequences (including arrays) and lets you select both key and value:
extension Sequence {
public func toDictionary<K: Hashable, V>(_ selector: (Iterator.Element) throws -> (K, V)?) rethrows -> [K: V] {
var dict = [K: V]()
for element in self {
if let (key, value) = try selector(element) {
dict[key] = value
}
}
return dict
}
}
Example:
let nameLookup = persons.toDictionary{($0.name, $0)}
Just do it simply,
let items = URLComponents(string: "https://im.qq.com?q=13&id=23")!.queryItems!
var dic = [String: Any?]()
items.foreach {
dic[$0.name] = $0.value
}
reduce is not very suitable,
let dic: [String: Any?] = items.reduce([:]) { (result: [String: Any?], item: URLQueryItem) -> [String: Any?] in
var r = result
r[item.name] = item.value // will create an copy of result!!!!!!
return r
}
As i understand from you're question you would like to convert to Array to Dictionary.
In my case i create extension for the Array and keys for the dictionary will be indexes of the Array.
Example:
var intArray = [2, 3, 5, 3, 2, 1]
extension Array where Element: Any {
var toDictionary: [Int:Element] {
var dictionary: [Int:Element] = [:]
for (index, element) in enumerate() {
dictionary[index] = element
}
return dictionary
}
}
let dic = intArray.toDictionary
Compatible with Swift 5 Standard Library (Xcode 10.2+ , iOS 12.2).
Here's an example of usage of an initializer init(uniqueKeysWithValues:)
The input let array: [String] = Locale.isoRegionCodes is an array of ISO31661-2 codes represented by a string.
let countryCodeAndName: [String: String] = Dictionary(uniqueKeysWithValues: Locale.isoRegionCodes.map { ($0, Locale.current.localizedString(forRegionCode: $0) ?? "")} )
Returned dictionary, will list all regions with ISO31661-2 code as a key and a localized region name as a value.
Output:
...
"PL":"Poland"
"DE":"Germany"
"FR":"France"
"ES":"Spain"
...
Example 2:
let dictionary: [String: String] = Dictionary(uniqueKeysWithValues: [ ("key1", "value1"), ("key2", "value2")] )
Output:
["key1": "value1", "key2": "value2"]
Important:
Precondition: The sequence must not have duplicate keys.
Code below will crash an app:
let digitWords = ["one", "two", "three", "four", "five", "five"]
let wordToValue = Dictionary(uniqueKeysWithValues: zip(digitWords, 1...6))
with:
Fatal error: Duplicate values for key: 'five'
If you want to follow the pattern set out by map and reduce in swift you could do something nice and functional like this:
extension Array {
func keyBy<Key: Hashable>(_ keyFor: (Element) -> Key) -> [Key: Element] {
var ret = [Key: Element]()
for item in self{
ret[keyFor(item)] = item
}
return ret
}
}
Usage:
struct Dog {
let id: Int
}
let dogs = [Dog(id: 1), Dog(id: 2), Dog(id: 3), Dog(id: 4)]
let dogsById = dogs.keyBy({ $0.id })
// [4: Dog(id: 4), 1: Dog(id: 1), 3: Dog(id: 3), 2: Dog(id: 2)]
Swift way:
extension Sequence {
func toDictionary<Key: Hashable>(with selectKey: (Element) -> Key) -> [Key: Element] {
reduce(into: [:]) { $0[selectKey($1)] = $1 }
}
}
// let arr = [Person(id: 1, name: "Alan")]
// arr.toDictionary { $0.id }
// ==
// [1: Person(id: 1, name: "Alan")]
I want to split an array like shown below.
let arrayToSplit = ["Europe|#|France|#|Paris", "Europe|#|Italy|#|Rome", "America|#|USA|#|Washington", "America|#|Canada|#|Ottawa"]
Into
let firstArray = ["Europe", "Europe", "America", "America"]
let secondArray = ["France", "Italy", "USA", "Canada"]
let thirdArray = ["Paris", "Rome", "Washington", "Ottawa"]
By separating into these three arrays I want to split the data income and present it in a UITableView.
Not the best solution, but with the expected result (hints are in the code comments):
let arrayToSplit = ["Europe|#|France|#|Paris", "Europe|#|Italy|#|Rome", "America|#|USA|#|Washington", "America|#|Canada|#|Ottawa"]
var firstArray = [String]()
var secondArray = [String]()
var thirdArray = [String]()
for element in arrayToSplit {
// new array with substrings divided by "|#|" e.g. ["Europe", "Europe", "America", "America"]
let newArray = element.componentsSeparatedByString("|#|")
firstArray.append(newArray[0])
secondArray.append(newArray[1])
thirdArray.append(newArray[2])
}
print("first array: \(firstArray)") // first array: ["Europe", "Europe", "America", "America"]
print("second array: \(secondArray)") // second array: ["France", "Italy", "USA", "Canada"]
print("third array: \(thirdArray)") // third array: ["Paris", "Rome", "Washington", "Ottawa"]
let arrayToSplit = ["Europe|#|France|#|Paris", "Europe|#|Italy|#|Rome", "America|#|USA|#|Washington", "America|#|Canada|#|Ottawa"]
print(arrayToSplit)
let firstArray : NSMutableArray = []
let secondArray : NSMutableArray = []
let thirdArray : NSMutableArray = []
for var i = 0; i < arrayToSplit.count; i++
{
let str : String = arrayToSplit[i] as String
let ary = str.characters.split{$0 == "|"}.map(String.init)
firstArray.addObject(ary[0])
secondArray.addObject(ary[2])
thirdArray.addObject(ary[4])
}
print(firstArray)
print(secondArray)
print(thirdArray)
let arrayToSplit = ["Europe|#|France|#|Paris", "Europe|#|Italy|#|Rome", "America|#|USA|#|Washington", "America|#|Canada|#|Ottawa"]
let arrayOfLists = arrayToSplit.map{
$0.componentsSeparatedByString("|#|")
}
let columns = Array(0..<3).map{ i in
arrayOfLists.map{ list in list[i]}
}
print(columns)
//[["Europe", "Europe", "America", "America"], ["France", "Italy", "USA", "Canada"], ["Paris", "Rome", "Washington", "Ottawa"]]
I have array and need to reverse it without Array.reverse method, only with a for loop.
var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
Swift 3:
var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames : [String] = Array(names.reversed())
print(reversedNames) // ["Asus", "Lenovo", "Sony", "Microsoft", "Apple"]
Here is #Abhinav 's answer translated to Swift 2.2 :
var names: [String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [String]()
for arrayIndex in (names.count - 1).stride(through: 0, by: -1) {
reversedNames.append(names[arrayIndex])
}
Using this code shouldn't give you any errors or warnings about the use deprecated of C-style for-loops or the use of --.
Swift 3 - Current:
let names: [String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [String]()
for arrayIndex in stride(from: names.count - 1, through: 0, by: -1) {
reversedNames.append(names[arrayIndex])
}
Alternatively, you could loop through normally and subtract each time:
let names = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
let totalIndices = names.count - 1 // We get this value one time instead of once per iteration.
var reversedNames = [String]()
for arrayIndex in 0...totalIndices {
reversedNames.append(names[totalIndices - arrayIndex])
}
Do you really need a for loop? If not, you can use reduce.
I guess that this is the shortest way to achieve it without reversed() method (Swift 3.0.1):
["Apple", "Microsoft", "Sony", "Lenovo", "Asus"].reduce([],{ [$1] + $0 })
Only need to make (names.count/2) passes through the array. No need to declare temporary variable, when doing the swap...it's implicit.
var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
let count = names.count
for i in 0..<count/2 {
(names[i],names[count - i - 1]) = (names[count - i - 1],names[i])
}
// Yields: ["Asus", "Lenovo", "Sony", "Microsoft", "Apple"]
There's also stride to generate a reversed index:
let names = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversed = [String]()
for index in (names.count - 1).stride(to: -1, by: -1) {
reversed.append(names[index])
}
It also works well with map:
let reversed = (names.count - 1).stride(to: -1, by: -1).map { names[$0] }
Note: stride starts its index at 1, not at 0, contrary to other Swift sequences.
However, to anyone reading this in the future: use .reverse() instead to actually reverse an array, it's the intended way.
var names:[String] = [ "A", "B", "C", "D", "E","F","G"]
var c = names.count - 1
var i = 0
while i < c {
swap(&names[i++],&names[c--])
}
Cristik
while i < c {
swap(&names[i],&names[c]
i += 1
c -= 1
}
Here you go:
var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [String]()
for var arrayIndex = names.count - 1 ; arrayIndex >= 0 ; arrayIndex-- {
reversedNames.append(names[arrayIndex])
}
Ignoring checks for emptiness..
var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [String]()
for name in names {
reversedNames.insert((name), at:0)
}
print(reversedNames)
Here is the most simpler way.
let names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [String]()
for name in names {
reversedNames.insert(name, at: 0)
}
Edited as generic
// Swap the first index with the last index.
// [1, 2, 3, 4, 5] -> pointer on one = array[0] and two = array.count - 1
// After first swap+loop increase the pointer one and decrease pointer two until
// conditional is not true.
func reverse<T>(with array: [T]) -> [T] {
var array = array
var first = 0
var last = array.count - 1
while first < last {
array.swapAt(first, last)
first += 1
last -= 1
}
return array
}
input-> [1, 2, 3, 4, 5] output ->[5, 4, 3, 2, 1]
input-> ["a", "b", "c", "d"] output->["d", "c", "b", "a"]
// Or a shorter version divide and conquer
func reversed<T>(with arr: [T]) -> [T] {
var arr = arr
(0..<arr.count / 2).forEach { i in
arr.swapAt(i, arr.count - i - 1)
}
return arr
}
The most efficient way is to swap the items at start- and endIndex and move the indices bidirectional to the middle. This is a generic version
extension Array {
mutating func upsideDown() {
if isEmpty { return }
var 👉 = startIndex
var 👈 = index(before: endIndex)
while 👉 < 👈 {
swapAt(👉, 👈)
formIndex(after: &👉)
formIndex(before: &👈)
}
}
}
Like this, maybe:
names = names.enumerate().map() { ($0.index, $0.element) }.sort() { $0.0 > $1.0 }.map() { $0.1 }
Oh, wait.. I have to use for loop, right? Then like this probably:
for (index, name) in names.enumerate().map({($0.index, $0.element)}).sort({$0.0 > $1.0}).map({$0.1}).enumerate() {
names[index] = name
}
Swift 5:
let names: [String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversenames: [String] = []
let count = names.count
for index in 0..<count {
reversenames.insert(names[count-index-1], at: index)
}
print(reversenames)
This will work with any sized array.
import Cocoa
var names:[String] = [ "A", "B", "C", "D", "E","F"]
var c = names.count - 1
for i in 0...(c/2-1) { swap(&names[i],&names[c-i]) }
print(names)
Here is how I did it and there is no warning for Swift 3
let names = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [String]()
for name in names.enumerate() {
let newIndex = names.count - 1 - name.index
reversedNames.append(names[newIndex])
}
or just simply
reversedNames = names.reverse()
Here the code for swift 3
let array = ["IOS A", "IOS B", "IOS C"]
for item in array.reversed() {
print("Found \(item)")
}
func reverse(array: inout [String]) {
if array.isEmpty { return }
var f = array.startIndex
var l = array.index(before: array.endIndex)
while f < l {
swap(array: &array, f, l)
array.formIndex(after: &f)
array.formIndex(before: &l)
}
}
private func swap( array: inout [String], _ i: Int, _ j: Int) {
guard i != j else { return }
let tmp = array[i]
array[i] = array[j]
array[j] = tmp
}
Or you can write extension of course
var rArray : [Int] = [2,5,6,8,3,8,9,10]
var ReArray = [Int]()
var a : Int = 1
func reversed (_ array: [Int]) -> [Int] {
for i in array {
ReArray.append(array[array.count-a])
a += 1
}
rArray = ReArray
return rArray
}
reversed(rArray)
print(rArray)
var arr = [1, 2, 3, 4, 5] // Array we want to reverse
var reverse: [Int]! // Array where we store reversed values
reverse = arr
for i in 0...(arr.count - 1) {
reverse[i] = arr.last! // Adding last value of original array at reverse[0]
arr.removeLast() // removing last value & repeating above step.
}
print("Reverse : \(reverse!)")
A more simple way :)
Recently I had an interview and I was asked this question, how to reverse an array without using reversed(). Here is my solution below:
func reverseArray( givenArray:inout [Int]) -> [Int] {
var reversedArray = [Int]()
while givenArray.count > 0 {
reversedArray.append(givenArray.removeLast())
}
return reversedArray
}
var array = [1,2,3,4,5,6,7]
var reversed = reverseArray(givenArray: &array)
First, need to find the middle of array. This method is faster than the linear time O(n) and slower than the constant time O(1) complexity.
func reverse<T>(items: [T]) -> [T] {
var reversed = items
let count = items.count
let middle = count / 2
for i in stride(from: 0, to: middle, by: 1) {
let first = items[i]
let last = items[count - 1 - i]
reversed[i] = last
reversed[count - 1 - i] = first
}
return reversed
}
Do it like this for reversed sorting.
let unsortedArray: [String] = ["X", "B", "M", "P", "Z"]
// reverse sorting
let reversedArray = unsortedArray.sorted() {$0 > $1}
print(reversedArray) // ["Z", "X", "P", "M", "B"]
I like simple codes.
var names:[String] = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
var reversedNames = [""]
for name in names {
reversedNames.insert(name, at: 0)
}
print(reversedNames)
var names = ["Apple", "Microsoft", "Sony", "Lenovo", "Asus"]
// 'while' loop
var index = 0
let totalIndices = names.count - 1
while index < names.count / 2 {
names.swapAt(index, totalIndices-index)
index += 1
}
// 'for' loop
for index in 0..<names.count/2 {
names.swapAt(index, names.count-index-1)
}
// output: "["Asus", "Lenovo", "Sony", "Microsoft", "Apple"]"
You can use the swift3 document:
let names = ["Chris", "Alex", "Ewa", "Barry", "Daniella"]
let reversedNames = names.sorted(by: >)
// reversedNames is equal to:
// ["Ewa", "Daniella", "Chris", "Barry", "Alex"]