I have searched for a while but couldn't find reasonable answer for this. I want to add/remove objects in one array to make effect in 2nd array which points to first array.
class Person
{
var name:String = ""
}
var arr1:[Person] = [Person]()
let p1 = Person()
p1.name = "Umair"
let p2 = Person()
p2.name = "Ali"
arr1.append(p1)
arr1.append(p2)
var arr2 = arr1
print("\(arr1.count)") //"2\n"
print("\(arr2.count)") //"2\n"
arr1.removeFirst()
print("\(arr1.count)") //"1\n"
print("\(arr2.count)") //"2\n"
Why changing arr1 does not affect arr2. Please help me out to accomplish this.
Arrays are value types. When we copy them, each copy is independent of the other. This is a virtue in Swift. What you are trying to do requires references so that effects on one can be seen by others. Try this code. Create a class (reference type) containing your data. Now changes to the container can be seen in the other.
class Person
{
var name: String
init(_ name: String) {
self.name = name
}
}
let p1 = Person("Umair")
let p2 = Person("Ali")
class Container {
var people = [Person]()
init(people: [Person]) {
self.people = people
}
}
let arr1 = Container(people: [p1, p2])
let arr2 = arr1
print(arr1.people)
print(arr2.people)
arr1.people.removeFirst()
print(arr1.people)
print(arr2.people)
Even if you're using Swift, you can still use NSArray.
Per Apple's documentation,
NSArray is an object representing a static ordered collection, for use instead of an Array constant in cases that require reference semantics.
The only downside is you'll have to import Foundation. This isn't a problem if you're creating an iOS or Mac app, as you're depending on it already.
Related
Apologize for a complete newbie question. This was the original array of Strings I wrote:
let fruit = ["apple1.jpg", "apple2.jpg", "apple3.jpg", ..... "apple10.jpg"]
First, I made a function in a separate Swift file (attached to the project) to replace above array, as the array's content might be changed based on several input factors later:
class Fruits {
let fruit = "apple"
func fruitName() -> [String] {
let arrayA = (1...10).map({ "\(fruit)\($0).jpg" })
return arrayA
}
}
}
This is everything written on Fruits.swift file. And then, back to original file, I wanted to replace the original let fruit = ["", "", ...] to something like let fruit = Fruits.fruitName() - by loading the returned arrayA. But it was a bit confusing to understand how to use returned String Array values in a different file, inside of a different Class bracket. I tried something like let fruits = Fruits(), let fruit = fruits.fruitName(), etc but it doesn't seem to successfully replace the original array code. I still need to create the constant let fruit = part. Is there any way to load the returned value in a separate file? Much appreciated. <3
If you want a property of a class to be directly accessible from anywhere in your code, you can make it static:
class Fruits {
static let fruit = "apple"
static func fruitName() -> [String] {
let arrayA = (1...10).map({ "\(fruit)\($0).jpg" })
return arrayA
}
}
// usage:
let fruits = Fruits.fruitName()
Depending on your specific situation, you could even not have a class and have a global function that takes the fruit as a parameter:
func fruitNames(fruit: String) -> [String] {
let arrayA = (1...10).map({ "\(fruit)\($0).jpg" })
return arrayA
}
// usage:
let fruits = fruitNames(fruit: "apple")
I ran into an issue with arrays in Swift. The problem is that it's a value type in Swift. I'm trying to find a workaround.
Here is the code that I have:
class Object: Codable{
var name : String?
}
var objects: Array<Object>?
objects = Array<Object>()
if var obj = objects { // <----- Creates a copy of array here
let o = Object()
o.name = "1"
objects?.append(o)
print(obj) //<----- this one is missing "o" object
print(objects)
}
I cannot use NSMutableArray because I have an array inside another codable class.
What's everybody's experience on this one? If somebody can share a solutions for that.
Getting used to arrays as value types isn't too tough really. If i were you my version of the code would just look like this
var objects: Array<Object>?
objects = Array<Object>()
if var unwrappedObjs = objects {
let o = Object()
o.name = "1"
unwrappedObjs.append(o)
objects = unwrappedObjs
}
or alternatively maybe this:
var objects: Array<Object>?
objects = Array<Object>()
if objects != nil {
let o = Object()
o.name = "1"
objects?.append(o)
}
Lastly you could always try making your own "ReferenceArray" class that wraps the array APIs and gives you reference semantics but that seems like overkill. Sooner rather than later, arrays as value types will seem natural to reason about.
bitwit already mentioned this to a point, but I think that your biggest mistake is simply not accepting the new object as the source. Unless it's important to retain the Array<Object>? you should replace it with the Array<Object> one.
var objects: Array<Object>?
objects = Array<Object>()
if var objects = objects { // <----- Creates a copy of array here
let o = Object()
o.name = "1"
objects.append(o) // objects is now the non-optional one
print(objects)
}
If it needs to be in the same scope, use guard:
var objects: Array<Object>?
objects = Array<Object>()
guard var objects = objects else { // <----- Creates a copy of array here
fatalError()
}
let o = Object()
o.name = "1"
objects.append(o) // objects is now the non-optional one
print(objects)
If you absolutely need an array to be referenced, you can make a container class:
public class ReferenceContainer<Element> {
public var element: Element
init(_ element: Element) {
self.element = element
}
}
I am currently struggling with obtaining a value from an array inside an array of dictionaries. Basically I want to grab the first "[0]" from an array stored inside an array of dictionaries. This is basically what I have:
var array = [[String:Any]]()
var hobbies:[String] = []
var dict = [String:Any]()
viewDidLoad Code:
dict["Name"] = "Andreas"
hobbies.append("Football", "Programming")
dict["Hobbies"] = hobbies
array.append(dict)
/// - However, I can only display the name, with the following code:
var name = array[0]["Name"] as! String
But I want to be able to display the first value in the array stored with the name, as well. How is this possible?
And yes; I know there's other options for this approach, but these values are coming from Firebase (child paths) - but I just need to find a way to display the array inside the array of dictionaries.
Thanks in advance.
If you know "Hobbies" is a valid key and its dictionary value is an array of String, then you can directly access the first item in that array with:
let hobby = (array[0]["Hobbies"] as! [String])[0]
but this will crash if "Hobbies" isn't a valid key or if the value isn't [String].
A safer way to access the array would be:
if let hobbies = array[0]["Hobbies"] as? [String] {
print(hobbies[0])
}
If you use a model class/struct things get easier
Given this model struct
struct Person {
let name: String
var hobbies: [String]
}
And this dictionary
var persons = [String:Person]()
This is how you put a person into the dictionary
let andreas = Person(name: "Andreas", hobbies: ["Football", "Programming"])
persons[andreas.name] = Andreas
And this is how you do retrieve it
let aPerson = persons["Andreas"]
Goal: I have two different classes, and two arrays containing members of each class. Using Swift 2.0, I would like to find the unique members of one array compared to the other based on specific attributes of each class.
Example:
class A {
var name: String
init(name: String) {
self.name = name
}
}
class B {
var title: String
init(title: String) {
self.title = title
}
}
let aArray = [A(name:"1"), A(name:"2"), A(name:"3"), A(name:"4")]
let bArray = [B(title:"1"), B(title:"2"), B(title:"5")]
So, I'm looking for some operation between aArray and bArray which returns the 3rd and 4th element of aArray, because they are uniquely in aArray, where the basis of comparison is the attributes A.name and B.title.
Of course, reversing the order of the operation would pick out the 3rd element of bArray, because it is uniquely in bArray.
I know I can accomplish the goal straightforwardly using a simple for loop, but I was hoping for something more elegant and more optimized. But if a for loop is as fast or faster than anything fancier, I'm happy to use it just as well.
I'm not sure fancy or elegant this code is, but, we could do something like this:
let mappedArray = bArray.map { $0.title }
let filteredArray = aArray.filter { !mappedArray.contains($0.name) }
So when we want the unique elements from aArray, we first map the elements from bArray to get an array of the value we want to actually compare:
let mappedArray = bArray.map { $0.title }
mappedArray is just an array of strings based on the title property of the objects in bArray.
Next, we use the filter method to filter objects from aArray. The filter method returns an array with objects that pass the test in our closure. The test we want to apply is objects that are not contained in the mapped array we just built.
let filteredArray = aArray.filter { !mappedArray.contains($0.name) }
If we want to do it the other way, just change a few things:
let mappedArray = aArray.map { $0.name }
let filteredArray = bArray.filter { !mappedArray.contains($0.title) }
I’m new to Swift and have been having some troubles figuring out some aspects of Arrays and Dictionaries.
I have an array of dictionaries, for which I have used Type Aliases - e.g.
typealias myDicts = Dictionary<String, Double>
var myArray : [myDicts] = [
["id":0,
"lat”:55.555555,
"lng”:-55.555555,
"distance":0],
["id":1,
"lat": 44.444444,
"lng”:-44.444444,
"distance":0]
]
I then want to iterate through the dictionaries in the array and change the “distance” key value. I did it like this:
for dict:myDicts in myArray {
dict["distance"] = 5
}
Or even specifically making sure 5 is a double with many different approaches including e.g.
for dict:myDicts in myArray {
let numberFive : Double = 5
dict["distance"] = numberFive
}
All my attempts cause an error:
#lvalue $T5' is not identical to '(String, Double)
It seems to be acting as if the Dictionaries inside were immutable “let” rather than “var”. So I randomly tried this:
for (var dict:myDicts) in myArray {
dict["distance"] = 5
}
This removes the error and the key is indeed assigned 5 within the for loop, but this doesn't seem to actually modify the array itself in the long run. What am I doing wrong?
The implicitly declared variable in a for-in loop in Swift is constant by default (let), that's why you can't modify it directly in the loop.
The for-in documentation has this:
for index in 1...5 {
println("\(index) times 5 is \(index * 5)")
}
In the example above, index is a constant whose value is automatically
set at the start of each iteration of the loop. As such, it does not
have to be declared before it is used. It is implicitly declared
simply by its inclusion in the loop declaration, without the need for
a let declaration keyword.
As you've discovered, you can make it a variable by explicitly declaring it with var. However, in this case, you're trying to modify a dictionary which is a struct and, therefore, a value type and it is copied on assignment. When you do dict["distance"] = 5 you're actually modifying a copy of the dictionary and not the original stored in the array.
You can still modify the dictionary in the array, you just have to do it directly by looping over the array by index:
for index in 0..<myArray.count {
myArray[index]["distance"] = 5
}
This way, you're sure to by modifying the original dictionary instead of a copy of it.
That being said, #matt's suggestion to use a custom class is usually the best route to take.
You're not doing anything wrong. That's how Swift works. You have two options:
Use NSMutableDictionary rather than a Swift dictionary.
Use a custom class instead of a dictionary. In a way this is a better solution anyway because it's what you should have been doing all along in a situation where all the dictionaries have the same structure.
The "custom class" I'm talking about would be a mere "value class", a bundle of properties. This was kind of a pain to make in Objective-C, but in Swift it's trivial, so I now do this a lot. The thing is that you can stick the class definition for your custom class anywhere; it doesn't need a file of its own, and of course in Swift you don't have the interface/implementation foo to grapple with, let alone memory management and other stuff. So this is just a few lines of code that you can stick right in with the code you've already got.
Here's an example from my own code:
class Model {
var task : NSURLSessionTask!
var im : UIImage!
var text : String!
var picurl : String!
}
We then have an array of Model and away we go.
So, in your example:
class MyDict : NSObject {
var id = 0.0
var lat = 0.0
var lng = 0.0
var distance = 0.0
}
var myArray = [MyDict]()
let d1 = MyDict()
d1.id = 0
d1.lat = 55.55
d1.lng = -55.55
d1.distance = 0
let d2 = MyDict()
d2.id = 0
d2.lat = 44.44
d2.lng = -44.44
d2.distance = 0
myArray = [d1,d2]
// now we come to the actual heart of the matter
for d in myArray {
d.distance = 5
}
println(myArray[0].distance) // it worked
println(myArray[1].distance) // it worked
Yes, the dictionary retrieved in the loop is immutable, hence you cannot change.
I'm afraid your last attempt just creates a mutable copy of it.
One possible workaround is to use NSMutableDictionary:
typealias myDicts = NSMutableDictionary
Have a class wrapper for the Swift dictionary or array.
class MyDictionary: NSObject {
var data : Dictionary<String,Any>!
init(_ data: Dictionary<String,Any>) {
self.data = data
}}
MyDictionary.data