With an array: How do I do indexOfObject or a proper containsObject?
I mean I know I could just bridge the Array to NSArray and do it there ^^
But there must be a 'native' way of doing this
P.S. for the containsObject I guess I could filter the array too but for indexOf?
You can use the built-in find, and thus avoid bridging to Objective-C — but only if your element type is Equatable. (If it isn't Equatable, you can make it so with a comparison function and an extension.)
Example:
func == (lhs:Piece,rhs:Piece) -> Bool {
return lhs.val == rhs.val
}
class Piece:Equatable,Printable {
var val : Int
var description : String { return String(val) }
init (_ v:Int) {
val = v
}
}
Now you can call find(arr,p) where arr is an Array<Piece> and p is a Piece.
Once you have this, you can develop utilities based on it. For example, here's a global function to remove an object from an array without bridging to Objective-C:
func removeObject<T:Equatable>(inout arr:Array<T>, object:T) -> T? {
if let found = find(arr,object) {
return arr.removeAtIndex(found)
}
return nil
}
And test it like this:
var arr = [Piece(1), Piece(2), Piece(3)]
removeObject(&arr,Piece(2))
println(arr)
You can do this for NSObject subclasses too. Example:
func == (v1:UIView, v2:UIView) -> Bool {
return v1.isEqual(v2)
}
extension UIView : Equatable {}
Now you can call find on an Array of UIView. It's sort of a pain in the butt, though, having to do this for every single class where you want to be able to use find on an Array of that class. I have filed an enhancement request with Apple requesting that all NSObject subclasses be considered Equatable and that == should fall back on isEqual: automatically.
EDIT Starting in Seed 3, this is automatic for UIView and other NSObject classes. So find now just works for them.
EDIT 2 Starting in Swift 2.0, indexOf will exist as a method:
let s = ["Manny", "Moe", "Jack"]
let ix = s.indexOf("Moe") // 1
Alternatively, it takes a function that returns Bool:
let ix2 = s.indexOf {$0.hasPrefix("J")} // 2
Again, this works only on collections of Equatable, since obviously you cannot locate a needle in a haystack unless you have a way of identifying a needle when you come to it.
EDIT 3 Swift 2.0 also introduces protocol extensions. This means I can rewrite my global function removeObject as a method!
For example:
extension RangeReplaceableCollectionType where Generator.Element : Equatable {
mutating func removeObject(object:Self.Generator.Element) {
if let found = self.indexOf(object) {
self.removeAtIndex(found)
}
}
}
Since Array adopts RangeReplaceableCollectionType, now I can write code like this:
var arr = [Piece(1), Piece(2), Piece(3)]
arr.removeObject(Piece(2))
Oh, happy day!
Its actually able to be done in Swift. To get the index use find(YourArray, ObjectToFind)
As I was told, this isn't available yet / I have to bridge it to NSArray
I don't like this and it feels dirty so I went and did this in an extension. that way it hides the usage of NSArray and allows apple to provide it later
import Foundation
extension Array {
func contains(object:AnyObject!) -> Bool {
if(self.isEmpty) {
return false
}
let array: NSArray = self.bridgeToObjectiveC();
return array.containsObject(object)
}
func indexOf(object:AnyObject!) -> Int? {
var index = NSNotFound
if(!self.isEmpty) {
let array: NSArray = self.bridgeToObjectiveC();
index = array.indexOfObject(object)
}
if(index == NSNotFound) {
return Optional.None;
}
return index
}
//#pragma mark KVC
func getKeyPath(keyPath: String!) -> AnyObject! {
return self.bridgeToObjectiveC().valueForKeyPath(keyPath);
}
}
https://gist.github.com/Daij-Djan/9d1c4b1233b4017f3b67
Apple provide an example of exactly this in the The Swift Programming Language book. Specifically, see the section on Type Constraints in Action (p621 in the iBook).
func findIndex<T: Equatable>(array: [T], valueToFind: T) -> Int? {
for (index, value) in enumerate(array) {
if value == valueToFind {
return index
}
}
return nil
}
Everything depends upon your type implementing Equatable.
The Swift Programming Language covers that and explains how to implement that protocol:
“The Swift standard library defines a protocol called Equatable, which
requires any conforming type to implement the equal to operator (==)
and the not equal to operator (!=) to compare any two values of that
type. ”
NSHipster has a couple of relevant posts on this subject:
Swift Default Protocol Implementations
Swift Comparison Protocols
I also found this answer very useful in implementing Equatable:
How do I implement Swift's Comparable protocol?
Alhough it mentions Comparable, Equatable is a subset and the explanation is good.
Excerpts above from: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/gb/jEUH0.l
One other option is to use filter:
haystack.filter({$0 == needle}).count > 0
This checks to see if array haystack contains object needle.
You can't. That's why NSArray is still there. However, the Apple documentation reads as follows about String and NSString:
Swift’s String type is bridged seamlessly to Foundation’s NSString
class. If you are working with the Foundation framework in Cocoa or
Cocoa Touch, the entire NSString API is available to call on any
String value you create, in addition to the String features described
in this chapter. You can also use a String value with any API that
requires an NSString instance.
Following that approach, the NSArray API should be available on Array, but it isn't because the native Swift Array is a primitive (most likely a struct or similar), so you have to "convert" it to an NSArray.
It appears that not all of the toll-free bridging from NS/CF space is in place. However, if you declare your array as an NSArray, it works fine:
let fruits: NSArray = [ "apple", "orange", "tomato (really?)" ]
let index = fruits.indexOfObject("orange")
println("Index of Orange: \(index)")
If your array elements are objects and you want to find an identical object in that array, you can use this function:
func findObject<C: CollectionType where C.Generator.Element: AnyObject>(domain: C, value: C.Generator.Element) -> Int? {
for (index, element) in enumerate(domain) {
if element === value {
return index
}
}
return nil
}
Related
I have a custom class called Place with 3 properties:
Name (String)
Category (String)
GeoPoint (CLLocationCoordinate2D)
I have an array of type [Place] of 100 objects and I want to check if there are duplicates on the GeoPoint property (just on this one).
How can I check duplicates of a specific property in an array of custom objects?
Thanks!
Although the accepted answer is good, I'd like to chip in.
There are two more ways to achieve what you want, and they both benefit from functionalities provided by SDK.
1 - Use Sets as Tj3n mentioned in a comment.
To achieve this you would need to make your Place conform to Hashable protocol.
class Place : Hashable {
var name = ""
var category = ""
var geoPoint: CLLocationCoordinate2D = CLLocationCoordinate2D()
var hashValue: Int {
get {
return geoPoint.longitude.hashValue &+ geoPoint.latitude.hashValue
}
}
}
func ==(lhs: Place, rhs: Place) -> Bool {
return lhs.geoPoint.latitude == rhs.geoPoint.latitude && lhs.geoPoint.longitude == rhs.geoPoint.longitude
}
The &+ operator in hashValue means "add, and don't crash at overflow". Using it is as straightforward as it can - let set = Set(yourArrayOfPlaces) - the set will contain only unique, in regard to geoPoint, places.
2 - Use KVC. While this is more of an Objective-C world, I find it a useful tool. To achieve this, you'd need to make Place inherit from NSObject. Then getting an array of unique places can be reduced to this one line :
let uniquePlaces = (yourPlacesArray as NSArray).value(forKeyPath: "#distinctUnionOfObjects.geoPoint")
You can do something like this:
var dict : [String : Int] = [:]
for place in arr {
if dict[place.GeoPoint] != nil { // Not in dictionary
if dict[place.GeoPoint] >= 1 { // If already there
return true // Duplicate
} else {
dict[place.GeoPoint]! += 1 // Increment instance
}
} else {
dict[place.GeoPoint] = 0 // Put in dictionary
}
}
return false // No duplicates
Where you loop through a [Place] array and check to see how many have the same GeoPoint. Then check to see if there's one there more than once.
Good day!
I am currently trying to learn programming swift and trying some examples of generics. Here is my example code
func findAll<T: Equatable>(arr: [T], _ elem: T) -> [Int] {
var indexesArr = [Int]()
var counter = 0
for i in arr {
if i == elem {
indexesArr.append(counter)
}
counter++
}
return indexesArr
}
findAll([5, 3, 7, 3, 9], 3)
findAll(["a", "b", "c", "b", "d"], 2.0)
It was supposed, that both arguments will be of the same type. But, unfortunately, as you can see I pass an array of string characters and a Double in my second function invocation and it still works! It returns an empty array []. No runtime or compile errors.
Please, explain me why it works and some workarounds maybe. Thank you!
Presumably you have import Cocoa or import Foundation in your code somewhere. If you remove that, you'll find that your code behaves as you're expecting.
The reason this happens is that importing Foundation causes Swift.Array to magically bridge to NSArray (aka [AnyObject]), and certain primitive value types to magically bridge to Foundation object types (like NSString and NSNumber). Once that happens, it's perfectly legal to call your function with parameters of types [AnyObject] and AnyObject.
I'm not aware of a good way around the magic conversion, but one way that works is to force your generic parameter to have a protocol that primitive value types conform to, but primitive values magically wrapped in Cocoa objects don't. One way to assure such is to create your own protocol:
public protocol NotAnyObject {}
extension Int: NotAnyObject {}
extension String: NotAnyObject {}
extension Double: NotAnyObject {}
func findAll<T: Equatable where T: NotAnyObject>(arr: [T], _ elem: T) -> [Int] { /*...*/ }
I'm not sure this is the best way, though... alternative proposals are welcome.
By the way, a more idiomatic/Swifty way to do something like this would be as a type extension (either a protocol extension, as below, or an extension on Array where Element: Equatable). You can even go functional-programming-style just for fun:
extension CollectionType where Generator.Element : Equatable {
public func allIndexesOf(element: Self.Generator.Element) -> [Self.Index] {
return zip(self.indices, self) // makes sequence of (index, element)
.filter { $0.1 == element }
.map { $0.0 }
}
}
Call it like this:
let threes = [5, 3, 7, 3, 9].allIndexesOf(3)
// returns [1, 3]
This is still subject to the same magic conversions issue, though:
let notThrees = ["twenty", "forty", "eight"].allIndexesOf[2.0]
// still compiles, returns []
So you'd still need to either use this extension only from Swift files that don't import Foundation, or apply a variant of the same hack as above, e.g.:
extension CollectionType where Generator.Element: Equatable,
Generator.Element: NotAnyObject { /*...*/ }
For the problem explanation see rickster's answer
Note that to solve problems like this, you can always just check how Swift libraries do it. The solution is to have both arguments as generics and using protocol constraints.
E.g. using SequenceType protocol instead of an Array.
func findAll<S: SequenceType, T: Equatable where S.Generator.Element == T>(arr: S, _ elem: T) -> [Int] {
var indexesArr = [Int]()
var counter = 0
for i in arr {
if i == elem {
indexesArr.append(counter)
}
counter++
}
return indexesArr
}
I am using a template project to try to build a new app. When I run the template project, I get an error saying: '[T] does not have a member named 'indexOf'.
The existing code in the Array+RemoveObject.swift doc is:
import Foundation
public func removeObject<T: Equatable>(object: T, inout fromArray array: [T])
{ let index = array.indexOf(object)
if let index = index {
array.removeAtIndex(index)
}
}
Is the problem the use of indexOf? The odd thing is that when I tried using the solution of someone who answered a similar question, I got around 100 errors from the bond framework.
You function on its own works fine for me (Swift 2.1.1, Xcode 7.2). It seems as if you want this function to be a method of a public class of yours. For a minimum working example, you need at least to wrap your removeObject() method within the class you want it to belong to. Note also that you needn't use a separate line for assigning the result from .indexOf(..) call (possibly nil), but can add assignment and nil check in a single if let statement.
public class MyArrayOperations {
// ...
static public func removeObject<T: Equatable>(object: T, inout fromArray array: [T]) {
if let index = array.indexOf(object) {
array.removeAtIndex(index)
}
}
}
var arr = ["1", "2","3"]
MyArrayOperations.removeObject("2", fromArray: &arr)
print(arr) // ["1", "3"]
Also note that you can explicitly state the same behaviour using two generics, in case you want the array itself to conform to some protocol. You then use one separate generic for the array type and one for its elements, thereafter specifying that the element type should conform to the Generator.Element type of the array. E.g.:
func removeObject<T: Equatable, U: _ArrayType where U.Generator.Element == T>(object: T, inout fromArray array: U) {
if let index = array.indexOf(object) {
array.removeAtIndex(index)
}
}
With this approach, you could add an additional protocol at type constraint for the array generic U in the function signature above, e.g.
func removeObject<T: Equatable, U: protocol<_ArrayType, MyProtocol> where U.Generator.Element == T>(object: T, inout fromArray array: [T]) { ...
This can be especially useful when "simulating" generic Array extensions that conforms to some protocol. See e.g. the following for such an example:
extend generic Array<T> to adopt protocol
I want to use function contains on Array of type AnyObject
import UIKit
var resultArray: Array<AnyObject> = Array()
resultArray.append(50)
resultArray.append(false)
resultArray.append("Test string")
let found = contains(resultArray, 50)
I get the error:
Type 'AnyObject -> L' does not conform to protocol 'IntegerLiteralConvertible'
I agree with the comments and other answer; AnyObject is not good practice, but if you really want to use AnyObject, you can treat your array of AnyObjects as an NSArray object and then use the function containsObject():
if (resultArray as NSArray).containsObject(AnyObjectOfAnyType) {
// Do something
}
You should probably be using Any in this example since you’re holding non-class types – otherwise you’ll be doing implicit conversion to NSThings.
But here’s a non-ObjC-interop way to do it:
let found = contains(resultArray) { ($0 as? Int) == 50 }
You can use the is keyword to differentiate between types, then use the piece of code by Airspeed Velocity above to do the search... Here's an example that you can modify and add extra types on if need be:
if resultArray[0] is String {
found = contains(resultArray) {
($0 as? String) == "hello"
}
} else if resultArray[0] is Int {
found = contains(resultArray) {
($0 as? Int) == 50
}
}
NOTE: You said your array will contain only 1 type at a time - this is important.
I have this for loop, p is a NSManagedObject, fathers is a to-many relationship, so I need to cast NSMutableOrderedSet to [Family] but it does not work, why?
for f in p.fathers as [Family] {
}
You can obtain an array representation of the set via the array property - then you can downcast it to the proper type and assign to a variable:
let families = p.fathers.array as [Family]
but of course you can also use it directly in the loop:
for f in p.fathers.array as [Family] {
....
}
Update
A forced downcast is now required using the ! operator, so the code above should be:
let families = p.fathers.array as! [Family]
The simple solution by Antonio should be used in this case. I'd just like to discuss this a bit more. If we try to enumerate an instance of 'NSMutableOrderedSet' in a 'for' loop, the compiler will complain:
error: type 'NSMutableOrderedSet' does not conform to protocol
'SequenceType'
When we write
for element in sequence {
// do something with element
}
the compiler rewrites it into something like this:
var generator = sequence.generate()
while let element = generator.next() {
// do something with element
}
'NS(Mutable)OrderedSet' doesn't have 'generate()' method i.e. it doesn't conform to the 'SequenceType' protocol. We can change that. First we need a generator:
public struct OrderedSetGenerator : GeneratorType {
private let orderedSet: NSMutableOrderedSet
public init(orderedSet: NSOrderedSet) {
self.orderedSet = NSMutableOrderedSet(orderedSet: orderedSet)
}
mutating public func next() -> AnyObject? {
if orderedSet.count > 0 {
let first: AnyObject = orderedSet.objectAtIndex(0)
orderedSet.removeObjectAtIndex(0)
return first
} else {
return nil
}
}
}
Now we can use that generator to make 'NSOrderedSet' conform to 'SequenceType':
extension NSOrderedSet : SequenceType {
public func generate() -> OrderedSetGenerator {
return OrderedSetGenerator(orderedSet: self)
}
}
'NS(Mutable)OrderedSet' can now be used in a 'for' loop:
let sequence = NSMutableOrderedSet(array: [2, 4, 6])
for element in sequence {
println(element) // 2 4 6
}
We could further implement 'CollectionType' and 'MutableCollectionType' (the latter for 'NSMutableOrderedSet' only) to make 'NS(Mutable)OrderedSet' behave like Swift's standard library collections.
Not sure if the above code follows the best practises as I'm still trying to wrap my head around details of all these protocols.