Related
I am trying to find an item index by searching a list. Does anybody know how to do that?
I see there is list.StartIndex and list.EndIndex but I want something like python's list.index("text").
As swift is in some regards more functional than object-oriented (and Arrays are structs, not objects), use the function "find" to operate on the array, which returns an optional value, so be prepared to handle a nil value:
let arr:Array = ["a","b","c"]
find(arr, "c")! // 2
find(arr, "d") // nil
Use firstIndex and lastIndex - depending on whether you are looking for the first or last index of the item:
let arr = ["a","b","c","a"]
let indexOfA = arr.firstIndex(of: "a") // 0
let indexOfB = arr.lastIndex(of: "a") // 3
tl;dr:
For classes, you might be looking for:
let index = someArray.firstIndex{$0 === someObject}
Full answer:
I think it's worth mentioning that with reference types (class) you might want to perform an identity comparison, in which case you just need to use the === identity operator in the predicate closure:
Swift 5, Swift 4.2:
let person1 = Person(name: "John")
let person2 = Person(name: "Sue")
let person3 = Person(name: "Maria")
let person4 = Person(name: "Loner")
let people = [person1, person2, person3]
let indexOfPerson1 = people.firstIndex{$0 === person1} // 0
let indexOfPerson2 = people.firstIndex{$0 === person2} // 1
let indexOfPerson3 = people.firstIndex{$0 === person3} // 2
let indexOfPerson4 = people.firstIndex{$0 === person4} // nil
Note that the above syntax uses trailing closures syntax, and is equivalent to:
let indexOfPerson1 = people.firstIndex(where: {$0 === person1})
Swift 4 / Swift 3 - the function used to be called index
Swift 2 - the function used to be called indexOf
* Note the relevant and useful comment by paulbailey about class types that implement Equatable, where you need to consider whether you should be comparing using === (identity operator) or == (equality operator). If you decide to match using ==, then you can simply use the method suggested by others (people.firstIndex(of: person1)).
You can filter an array with a closure:
var myList = [1, 2, 3, 4]
var filtered = myList.filter { $0 == 3 } // <= returns [3]
And you can count an array:
filtered.count // <= returns 1
So you can determine if an array includes your element by combining these:
myList.filter { $0 == 3 }.count > 0 // <= returns true if the array includes 3
If you want to find the position, I don't see fancy way, but you can certainly do it like this:
var found: Int? // <= will hold the index if it was found, or else will be nil
for i in (0..x.count) {
if x[i] == 3 {
found = i
}
}
EDIT
While we're at it, for a fun exercise let's extend Array to have a find method:
extension Array {
func find(includedElement: T -> Bool) -> Int? {
for (idx, element) in enumerate(self) {
if includedElement(element) {
return idx
}
}
return nil
}
}
Now we can do this:
myList.find { $0 == 3 }
// returns the index position of 3 or nil if not found
Swift 5
func firstIndex(of element: Element) -> Int?
var alphabets = ["A", "B", "E", "D"]
Example1
let index = alphabets.firstIndex(where: {$0 == "A"})
Example2
if let i = alphabets.firstIndex(of: "E") {
alphabets[i] = "C" // i is the index
}
print(alphabets)
// Prints "["A", "B", "C", "D"]"
While indexOf() works perfectly, it only returns one index.
I was looking for an elegant way to get an array of indexes for elements which satisfy some condition.
Here is how it can be done:
Swift 3:
let array = ["apple", "dog", "log"]
let indexes = array.enumerated().filter {
$0.element.contains("og")
}.map{$0.offset}
print(indexes)
Swift 2:
let array = ["apple", "dog", "log"]
let indexes = array.enumerate().filter {
$0.element.containsString("og")
}.map{$0.index}
print(indexes)
in Swift 4.2
.index(where:) was changed to .firstIndex(where:)
array.firstIndex(where: {$0 == "person1"})
For custom class, you need to implement the Equatable protocol.
import Foundation
func ==(l: MyClass, r: MyClass) -> Bool {
return l.id == r.id
}
class MyClass: Equtable {
init(id: String) {
self.msgID = id
}
let msgID: String
}
let item = MyClass(3)
let itemList = [MyClass(1), MyClass(2), item]
let idx = itemList.indexOf(item)
printl(idx)
In Swift 4, the firstIndex method can be used. An example of using the == equality operator to find an object in an array by its id:
let index = array.firstIndex{ $0.id == object.id }
note this solution avoids your code needing to conform to the Equitable protocol as we're comparing the property and not the entire object
Also, a note about == vs === since many of the answers posted so far have differed in their usage:
== is the equality operator. It checks if values are equal.
=== is the identity operator. It checks whether two instances of a class point to the same memory. This is different from equality, because two objects that were created independently using the same values will be considered equal using == but not === because they are different objects. (Source)
It would be worth it to read more on these operators from Swift's documentation.
Just use firstIndex method.
array.firstIndex(where: { $0 == searchedItem })
Update for Swift 2:
sequence.contains(element): Returns true if a given sequence (such as
an array) contains the specified element.
Swift 1:
If you're looking just to check if an element is contained inside an array, that is, just get a boolean indicator, use contains(sequence, element) instead of find(array, element):
contains(sequence, element): Returns true if a given sequence (such as
an array) contains the specified element.
See example below:
var languages = ["Swift", "Objective-C"]
contains(languages, "Swift") == true
contains(languages, "Java") == false
contains([29, 85, 42, 96, 75], 42) == true
if (contains(languages, "Swift")) {
// Use contains in these cases, instead of find.
}
Swift 4. If your array contains elements of type [String: AnyObject]. So to find the index of element use the below code
var array = [[String: AnyObject]]()// Save your data in array
let objectAtZero = array[0] // get first object
let index = (self.array as NSArray).index(of: objectAtZero)
Or If you want to found index on the basis of key from Dictionary. Here array contains Objects of Model class and I am matching id property.
let userId = 20
if let index = array.index(where: { (dict) -> Bool in
return dict.id == userId // Will found index of matched id
}) {
print("Index found")
}
OR
let storeId = Int(surveyCurrent.store_id) // Accessing model key value
indexArrUpTo = self.arrEarnUpTo.index { Int($0.store_id) == storeId }! // Array contains models and finding specific one
In Swift 4, if you are traversing through your DataModel array, make sure your data model conforms to Equatable Protocol , implement the lhs=rhs method , and only then you can use ".index(of" . For example
class Photo : Equatable{
var imageURL: URL?
init(imageURL: URL){
self.imageURL = imageURL
}
static func == (lhs: Photo, rhs: Photo) -> Bool{
return lhs.imageURL == rhs.imageURL
}
}
And then,
let index = self.photos.index(of: aPhoto)
For (>= swift 4.0)
It's rather very simple.
Consider the following Array object.
var names: [String] = ["jack", "rose", "jill"]
In order to obtain the index of the element rose, all you have to do is:
names.index(of: "rose") // returns 1
Note:
Array.index(of:) returns an Optional<Int>.
nil implies that the element isn't present in the array.
You might want to force-unwrap the returned value or use an if-let to get around the optional.
Swift 2.1
var array = ["0","1","2","3"]
if let index = array.indexOf("1") {
array.removeAtIndex(index)
}
print(array) // ["0","2","3"]
Swift 3
var array = ["0","1","2","3"]
if let index = array.index(of: "1") {
array.remove(at: index)
}
array.remove(at: 1)
In Swift 2 (with Xcode 7), Array includes an indexOf method provided by the CollectionType protocol. (Actually, two indexOf methodsāone that uses equality to match an argument, and another that uses a closure.)
Prior to Swift 2, there wasn't a way for generic types like collections to provide methods for the concrete types derived from them (like arrays). So, in Swift 1.x, "index of" is a global function... And it got renamed, too, so in Swift 1.x, that global function is called find.
It's also possible (but not necessary) to use the indexOfObject method from NSArray... or any of the other, more sophisticated search meth dis from Foundation that don't have equivalents in the Swift standard library. Just import Foundation (or another module that transitively imports Foundation), cast your Array to NSArray, and you can use the many search methods on NSArray.
Any of this solution works for me
This the solution i have for Swift 4 :
let monday = Day(name: "M")
let tuesday = Day(name: "T")
let friday = Day(name: "F")
let days = [monday, tuesday, friday]
let index = days.index(where: {
//important to test with === to be sure it's the same object reference
$0 === tuesday
})
You can also use the functional library Dollar to do an indexOf on an array as such http://www.dollarswift.org/#indexof-indexof
$.indexOf([1, 2, 3, 1, 2, 3], value: 2)
=> 1
If you are still working in Swift 1.x
then try,
let testArray = ["A","B","C"]
let indexOfA = find(testArray, "A")
let indexOfB = find(testArray, "B")
let indexOfC = find(testArray, "C")
For SWIFT 3 you can use a simple function
func find(objecToFind: String?) -> Int? {
for i in 0...arrayName.count {
if arrayName[i] == objectToFind {
return i
}
}
return nil
}
This will give the number position, so you can use like
arrayName.remove(at: (find(objecToFind))!)
Hope to be useful
In Swift 4/5, use "firstIndex" for find index.
let index = array.firstIndex{$0 == value}
Swift 4
For reference types:
extension Array where Array.Element: AnyObject {
func index(ofElement element: Element) -> Int? {
for (currentIndex, currentElement) in self.enumerated() {
if currentElement === element {
return currentIndex
}
}
return nil
}
}
In case somebody has this problem
Cannot invoke initializer for type 'Int' with an argument list of type '(Array<Element>.Index?)'
jsut do this
extension Int {
var toInt: Int {
return self
}
}
then
guard let finalIndex = index?.toInt else {
return false
}
SWIFT 4
Let's say you want to store a number from the array called cardButtons into cardNumber, you can do it this way:
let cardNumber = cardButtons.index(of: sender)
sender is the name of your button
I'm pretty new to JavaScript and need to create a JSON with number of keys and values (pushed into the variable newWord), without separating them. The thing is that I don't know what would be the length it in advenced (for that I am using a for loop to push each of the keys names and values):
let langName = document.querySelectorAll('.langName');
let langInput = document.querySelectorAll('.langInput');
let newWord = new Array()
for (let i = 0; i < langName.length; i++) {
let l = langName[i].value;
let w = langInput[i].value
newWord.push({[l]: w})
}
firebase.database().ref(`content/words/`).push(
newWord
)
So, my result right now is:
While my desired result would be:
Does anyone know how do I get rid of the indexes (0, 1) and push a string key with a string value?
Edit: I want the for loop to add to the same object in this array, instead of creating a new object inside of it.
Thanks! š
push is used to insert in a list in firebase database. Using set, you can store as key-value objects.
let langName = document.querySelectorAll('.langName');
let langInput = document.querySelectorAll('.langInput');
let newWord = {};
for (let i = 0; i < langName.length; i++) {
let l = langName[i].value;
let w = langInput[i].value
newWord[l] = w;
}
firebase.database().ref(`content/words/`).set(
newWord
)
I am trying to change my string value in an array after shuffling another array, how am i to do this?
Example:
var array1 = [1,2,3,4,5,6]
var stringarray = ["\\(array1[0]) = 1")
array1.shuffle()
print(stringarray)
How am i to change the original stringarray value to the new shuffled value?
Thank you
The task:
#IBAction func nextQuestion(_ sender: Any) {
if levelSelected == 1 {
questionLabel.text = standardRules.randomElement()
}
players.shuffle()
print(players)
standardRules has a string value that takes the value of players[0]
Essentially what i am trying to do is this:
I am trying to grab 2 random values that are not the same in a string like this
var players = ["Jack, John, Michael, Peter"]
var playersArray = ["\(players.randomElement) and \(players.randomElement) has to battle")
How am i to do this, so it grabs 2 different values?
You could make it very easy by this code :
var players = ["Jack", "John", "Michael", "Peter"]
// get the first random element
var random1 = players.randomElement()
//delete that element so you can't duplicate it
players = players.filter{$0 != random1}
//get your second radom element
var random2 = players.randomElement()
//add your element again
players.append(random1!)
Looks like you're missing some core concepts of the Swift language. When you create your stringarray it makes a call of array1.description and stores the result into an array. From that point any modifications of the original array will not change anything in stringarray.
So if you want to pick two different players from an array you need to do something like that:
let index1 = Int.random(in: (0 ..< players.count))
var index2: Int
repeat {
index2 = Int.random(in: (0 ..< players.count))
} while index1 == index2
let matchText = "\(players[index1]) and \(players[index2] has to battle)"
I would try replacing:
var stringarray = ["\\(array1[0]) = 1")
array1.shuffle()
with:
var stringarray = array1.shuffle()
I have two arrays:
GlobalArray:Array(Int,Array[String]) and SpecificArray:Array(Int,Int).
The first Int in both of them is a key and I would like to get the element corresponding to that key from the GlobalArray.
In pseudocode:
val v1
For each element of SpecificArray
Get the corresponding element from GlobalArray to use its Array[String]
If (sum <= 100)
for each String of the Array
update v1
// ... some calculation
sum += 1
println (v1)
I know using .map() I could go through each position of the SpecificArray, but so far I was able to do this:
SpecificArray.map{x => val in_global = GlobalArray.filter(e => (e._1 == x._1))
// I don't know how to follow
}
How about something like below, I would prefer to for comprehension code which has better readability.
var sum:Int = 0
var result:String = ""
for {
(k1,v1) <- SpecificArray //v1 is the second int from specific array
(k2,values) <- GlobalArray if k1 == k2 //values is the second array from global array
value <- values if sum < 100 //value is one value frome the values
_ = {sum+=1; result += s"(${v1}=${value})"} //Update something here with the v1 and value
} yield ()
println(result)
Note needs more optimization
Convert GlobalArray to Map for faster lookup.
val GlobalMap = GlobalArray.toMap
SpecificArray.flatMap(x => GlobalMap(x._1))
.foldLeft(0)((sum:Int, s:String) => {
if(sum<=100) {
// update v1
// some calculation
}
sum+1
})
If not all keys of SpecificArray is present in GlobalMap then use GlobalMap.getOrElse(x._1, Array())
How sum affects the logic and what exactly is v1 is not clear from your code, but it looks like you do search through GlobalArray many times. If this is so, it makes sense to convert this array into a more search-friendly data structure: Map. You can do it like this
val globalMap = GlobalArray.toMap
and then you may use to join the strings like this
println(SpecificArray.flatMap({case (k,v) => globalMap(k).map(s => (k,v,s))}).toList)
If all you need is strings you may use just
println(SpecificArray.flatMap({case (k,v) => globalMap(k)}).toList)
Note that this code assumes that for every key in the SpecificArray there will be a matching key in the GlobalArray. If this is not the case, you should use some other method to access the Map like getOrElse:
println(SpecificArray.flatMap({case (k,v) => globalMap.getOrElse(k, Array()).map(s => (k,v,s))}).toList)
Update
If sum is actually count and it works for whole "joined" data rather than for each key in the SpecificArray, you may use take instead of it. Code would go like this:
val joined = SpecificArray2.flatMap({case (k,v) => globalMap.getOrElse(k, Array()).map(s => (s,v))})
.take(100) // use take instead of sum
And then you may use joined whatever way you want. And updated demo that builds v1 as joined string of form v1 += String_of_GlobalArray + " = " + 2nd_Int_of_SpecificArray is here. The idea is to use mkString instead of explicit variable update.
I am trying to find an item index by searching a list. Does anybody know how to do that?
I see there is list.StartIndex and list.EndIndex but I want something like python's list.index("text").
As swift is in some regards more functional than object-oriented (and Arrays are structs, not objects), use the function "find" to operate on the array, which returns an optional value, so be prepared to handle a nil value:
let arr:Array = ["a","b","c"]
find(arr, "c")! // 2
find(arr, "d") // nil
Use firstIndex and lastIndex - depending on whether you are looking for the first or last index of the item:
let arr = ["a","b","c","a"]
let indexOfA = arr.firstIndex(of: "a") // 0
let indexOfB = arr.lastIndex(of: "a") // 3
tl;dr:
For classes, you might be looking for:
let index = someArray.firstIndex{$0 === someObject}
Full answer:
I think it's worth mentioning that with reference types (class) you might want to perform an identity comparison, in which case you just need to use the === identity operator in the predicate closure:
Swift 5, Swift 4.2:
let person1 = Person(name: "John")
let person2 = Person(name: "Sue")
let person3 = Person(name: "Maria")
let person4 = Person(name: "Loner")
let people = [person1, person2, person3]
let indexOfPerson1 = people.firstIndex{$0 === person1} // 0
let indexOfPerson2 = people.firstIndex{$0 === person2} // 1
let indexOfPerson3 = people.firstIndex{$0 === person3} // 2
let indexOfPerson4 = people.firstIndex{$0 === person4} // nil
Note that the above syntax uses trailing closures syntax, and is equivalent to:
let indexOfPerson1 = people.firstIndex(where: {$0 === person1})
Swift 4 / Swift 3 - the function used to be called index
Swift 2 - the function used to be called indexOf
* Note the relevant and useful comment by paulbailey about class types that implement Equatable, where you need to consider whether you should be comparing using === (identity operator) or == (equality operator). If you decide to match using ==, then you can simply use the method suggested by others (people.firstIndex(of: person1)).
You can filter an array with a closure:
var myList = [1, 2, 3, 4]
var filtered = myList.filter { $0 == 3 } // <= returns [3]
And you can count an array:
filtered.count // <= returns 1
So you can determine if an array includes your element by combining these:
myList.filter { $0 == 3 }.count > 0 // <= returns true if the array includes 3
If you want to find the position, I don't see fancy way, but you can certainly do it like this:
var found: Int? // <= will hold the index if it was found, or else will be nil
for i in (0..x.count) {
if x[i] == 3 {
found = i
}
}
EDIT
While we're at it, for a fun exercise let's extend Array to have a find method:
extension Array {
func find(includedElement: T -> Bool) -> Int? {
for (idx, element) in enumerate(self) {
if includedElement(element) {
return idx
}
}
return nil
}
}
Now we can do this:
myList.find { $0 == 3 }
// returns the index position of 3 or nil if not found
Swift 5
func firstIndex(of element: Element) -> Int?
var alphabets = ["A", "B", "E", "D"]
Example1
let index = alphabets.firstIndex(where: {$0 == "A"})
Example2
if let i = alphabets.firstIndex(of: "E") {
alphabets[i] = "C" // i is the index
}
print(alphabets)
// Prints "["A", "B", "C", "D"]"
While indexOf() works perfectly, it only returns one index.
I was looking for an elegant way to get an array of indexes for elements which satisfy some condition.
Here is how it can be done:
Swift 3:
let array = ["apple", "dog", "log"]
let indexes = array.enumerated().filter {
$0.element.contains("og")
}.map{$0.offset}
print(indexes)
Swift 2:
let array = ["apple", "dog", "log"]
let indexes = array.enumerate().filter {
$0.element.containsString("og")
}.map{$0.index}
print(indexes)
in Swift 4.2
.index(where:) was changed to .firstIndex(where:)
array.firstIndex(where: {$0 == "person1"})
For custom class, you need to implement the Equatable protocol.
import Foundation
func ==(l: MyClass, r: MyClass) -> Bool {
return l.id == r.id
}
class MyClass: Equtable {
init(id: String) {
self.msgID = id
}
let msgID: String
}
let item = MyClass(3)
let itemList = [MyClass(1), MyClass(2), item]
let idx = itemList.indexOf(item)
printl(idx)
In Swift 4, the firstIndex method can be used. An example of using the == equality operator to find an object in an array by its id:
let index = array.firstIndex{ $0.id == object.id }
note this solution avoids your code needing to conform to the Equitable protocol as we're comparing the property and not the entire object
Also, a note about == vs === since many of the answers posted so far have differed in their usage:
== is the equality operator. It checks if values are equal.
=== is the identity operator. It checks whether two instances of a class point to the same memory. This is different from equality, because two objects that were created independently using the same values will be considered equal using == but not === because they are different objects. (Source)
It would be worth it to read more on these operators from Swift's documentation.
Just use firstIndex method.
array.firstIndex(where: { $0 == searchedItem })
Update for Swift 2:
sequence.contains(element): Returns true if a given sequence (such as
an array) contains the specified element.
Swift 1:
If you're looking just to check if an element is contained inside an array, that is, just get a boolean indicator, use contains(sequence, element) instead of find(array, element):
contains(sequence, element): Returns true if a given sequence (such as
an array) contains the specified element.
See example below:
var languages = ["Swift", "Objective-C"]
contains(languages, "Swift") == true
contains(languages, "Java") == false
contains([29, 85, 42, 96, 75], 42) == true
if (contains(languages, "Swift")) {
// Use contains in these cases, instead of find.
}
Swift 4. If your array contains elements of type [String: AnyObject]. So to find the index of element use the below code
var array = [[String: AnyObject]]()// Save your data in array
let objectAtZero = array[0] // get first object
let index = (self.array as NSArray).index(of: objectAtZero)
Or If you want to found index on the basis of key from Dictionary. Here array contains Objects of Model class and I am matching id property.
let userId = 20
if let index = array.index(where: { (dict) -> Bool in
return dict.id == userId // Will found index of matched id
}) {
print("Index found")
}
OR
let storeId = Int(surveyCurrent.store_id) // Accessing model key value
indexArrUpTo = self.arrEarnUpTo.index { Int($0.store_id) == storeId }! // Array contains models and finding specific one
In Swift 4, if you are traversing through your DataModel array, make sure your data model conforms to Equatable Protocol , implement the lhs=rhs method , and only then you can use ".index(of" . For example
class Photo : Equatable{
var imageURL: URL?
init(imageURL: URL){
self.imageURL = imageURL
}
static func == (lhs: Photo, rhs: Photo) -> Bool{
return lhs.imageURL == rhs.imageURL
}
}
And then,
let index = self.photos.index(of: aPhoto)
For (>= swift 4.0)
It's rather very simple.
Consider the following Array object.
var names: [String] = ["jack", "rose", "jill"]
In order to obtain the index of the element rose, all you have to do is:
names.index(of: "rose") // returns 1
Note:
Array.index(of:) returns an Optional<Int>.
nil implies that the element isn't present in the array.
You might want to force-unwrap the returned value or use an if-let to get around the optional.
Swift 2.1
var array = ["0","1","2","3"]
if let index = array.indexOf("1") {
array.removeAtIndex(index)
}
print(array) // ["0","2","3"]
Swift 3
var array = ["0","1","2","3"]
if let index = array.index(of: "1") {
array.remove(at: index)
}
array.remove(at: 1)
In Swift 2 (with Xcode 7), Array includes an indexOf method provided by the CollectionType protocol. (Actually, two indexOf methodsāone that uses equality to match an argument, and another that uses a closure.)
Prior to Swift 2, there wasn't a way for generic types like collections to provide methods for the concrete types derived from them (like arrays). So, in Swift 1.x, "index of" is a global function... And it got renamed, too, so in Swift 1.x, that global function is called find.
It's also possible (but not necessary) to use the indexOfObject method from NSArray... or any of the other, more sophisticated search meth dis from Foundation that don't have equivalents in the Swift standard library. Just import Foundation (or another module that transitively imports Foundation), cast your Array to NSArray, and you can use the many search methods on NSArray.
Any of this solution works for me
This the solution i have for Swift 4 :
let monday = Day(name: "M")
let tuesday = Day(name: "T")
let friday = Day(name: "F")
let days = [monday, tuesday, friday]
let index = days.index(where: {
//important to test with === to be sure it's the same object reference
$0 === tuesday
})
You can also use the functional library Dollar to do an indexOf on an array as such http://www.dollarswift.org/#indexof-indexof
$.indexOf([1, 2, 3, 1, 2, 3], value: 2)
=> 1
If you are still working in Swift 1.x
then try,
let testArray = ["A","B","C"]
let indexOfA = find(testArray, "A")
let indexOfB = find(testArray, "B")
let indexOfC = find(testArray, "C")
For SWIFT 3 you can use a simple function
func find(objecToFind: String?) -> Int? {
for i in 0...arrayName.count {
if arrayName[i] == objectToFind {
return i
}
}
return nil
}
This will give the number position, so you can use like
arrayName.remove(at: (find(objecToFind))!)
Hope to be useful
In Swift 4/5, use "firstIndex" for find index.
let index = array.firstIndex{$0 == value}
Swift 4
For reference types:
extension Array where Array.Element: AnyObject {
func index(ofElement element: Element) -> Int? {
for (currentIndex, currentElement) in self.enumerated() {
if currentElement === element {
return currentIndex
}
}
return nil
}
}
In case somebody has this problem
Cannot invoke initializer for type 'Int' with an argument list of type '(Array<Element>.Index?)'
jsut do this
extension Int {
var toInt: Int {
return self
}
}
then
guard let finalIndex = index?.toInt else {
return false
}
SWIFT 4
Let's say you want to store a number from the array called cardButtons into cardNumber, you can do it this way:
let cardNumber = cardButtons.index(of: sender)
sender is the name of your button