How to get last element on Swift ?
var test: [Int:String] = [Int:String]()
test[1] = "CCC"
test[3] = "AAA"
test[2] = "BBB"
I am trying to get Int 3. I try to use endIndex like this
let (key,value) = test.endIndex
and
print(test.endIndex)
but it does not work.
You haven't been very clear, but I think you're trying to get the last element of an ordered dictionary. Swift's native Dictionary type is unordered, so you will have to manually sort it:
test.keys.sort().last.map({ ($0, test[$0]!) })
In your specific case, the code above will return Optional((3, "AAA")) (i.e. typed Optional<(Key, Value )>).
Related
I have array of Any objects called timestamps, in which first object is string, and rest objects are Int. What i want is, to drop first element and treat rest of array as Array of Int objects..
I tried:
let timestamps = xAxisData.dropFirst()
if let timestamps = timestamps as? Array<Int> {
}
It compile, but it says - Cast from 'ArraySlice<Any>' to unrelated type 'Array<Int>' always fails
I could possibly iterate through array and create new temporary array with check every element whether it Int or not, but i think there is a better cleaner way?
You need to create an Array from the ArraySlice created by dropFirst.
let timestamps = Array(xAxisData.dropFirst())
if let timestamps = timestamps as? [Int] {
}
I like to use something like a flatMap so no matter were the non-Int values are in the array they are not consider for the resulting array.
let originalArray:[Any] = ["No int", 2, 3, "Also not int", 666, 423]
let intArray:[Int] = originalArray.flatMap { $0 as? Int }
print(intArray)
Will print this:
[2, 3, 666, 423]
So in your case you could do something like:
let timestamps = xAxisData.flatMap { $0 as? Int }
As stated by Steve Madsen in the comment below, if you are using Swift 4.1 or newer Apple suggest to used compactMap for getting rid of optional nils so that specific use of flatMap is deprecated.
let timestamps = xAxisData.compactMap { $0 as? Int }
Here is another method to convert a subset of an array with mixed types to something more specific:
let intArray = anyArray.compactMap { $0 as? Int }
I'm trying to create a set of random exercises. I have made my struct Hashable and Equatable following the tutorial here https://medium.com/#JoyceMatos/hashable-protocols-in-swift-baf0cabeaebd and that is working fine so it's ready to be put in a Set<>.
When I use an Array to collect the workout exercises, as per below, it works fine. But when I switch to a Set<> I get an error "cannot convert value of type [_] to specified type 'Set'. What is it about 'Sets' that mean you can't map in the same way as an Array?
func generateWorkout() {
let allPossibleExercises = masterExerciseArray
let numberOfExercisesKey = Int(arc4random_uniform(4)+3)
//error triggers on the line below if I switch [WorkoutExercise]
//for Set<WorkoutExercise> (which conforms to Hashable/Equatable
let workoutSet : [WorkoutExercise] = (1...numberOfExercisesKey).map { _ in
let randomKey = Int(arc4random_uniform(UInt32(allPossibleExercises.count)))
return WorkoutExerciseGenerator( name: allPossibleExercises[randomKey].name,
maxReps: allPossibleExercises[randomKey].maxReps).generate()
}
print (workoutSet)
}
There is an answer here with a similar error message Cannot convert value of type '[_]' to specified type 'Array' but my array wouldn't be empty as in this example so I don't think this is the same root cause?
UPDATE : for anyone having the same problem, you can use Array but then simply convert the Array to a Set afterwards if the correct elements are Hashable/Equatable
If creating the array works create the array and then make the Set from the array. If all involved objects conform to Hashable this is supposed to work.
func generateWorkout() {
let allPossibleExercises = masterExerciseArray
let numberOfExercisesKey = Int(arc4random_uniform(4)+3)
let workoutArray : [WorkoutExercise] = (1...numberOfExercisesKey).map { _ in
let randomKey = Int(arc4random_uniform(UInt32(allPossibleExercises.count)))
return WorkoutExerciseGenerator( name: allPossibleExercises[randomKey].name,
maxReps: allPossibleExercises[randomKey].maxReps).generate()
}
let workoutSet = Set(workoutArray)
print (workoutSet)
}
var someDict = [String:Any]()
someDict["foo"] = ["hello"]
(someDict["foo"] as? [String])?.append("goodbye") // error here
I am trying to add a value to an existing dictionary containing an array. The dictionary also contains other non-array values, so it has to have value type Any. The problem is that, when I do this, I get an error Cannot use mutating member on immutable value of type '[String]'. Some Googling turned up a few references such as this suggesting that arrays within dictionaries are always immutable, but the compiler doesn't complain if I do this:
var someDict = [String:[String]]()
someDict["foo"] = ["hello"]
someDict["foo"]?.append("goodbye")
so I suspect that information is outdated and it's something specific to the downcasting. Is there any way I can get around this without copying and re-assigning the entire dictionary value?
Yes, it is related the the downcasting. Try this instead:
var someDict = [String:Any]()
someDict["foo"] = ["hello"]
if var arr = someDict["foo"] as? [String] {
arr.append("goodbye")
someDict["foo"] = arr
}
I've been through similar questions but still do not understand why my code is throwing an error.
var dict = [String:AnyObject]()
dict["participants"] = ["foo", "bar"]
dict["participants"][0] = "baz"
The error is on line 3: (String: AnyObject) does not have a member named 'subscript'
I'm setting the participants key to an array and then trying to update the first element of it without any luck. The code above is shortened for example purposes, but I am using [String:AnyObject] because it is not only arrays that are stored in the dictionary.
It's probably something really trivial but I am still new to Swift. Thanks for any help in advance!
The error message tells you exactly what the problem is. Your dictionary values are typed as AnyObject. I know you know that this value is a string array, but Swift does not know that; it knows only what you told it, that this is an AnyObject. But AnyObject can't be subscripted (in fact, you can't do much with it at all). If you want to use subscripting, you need to tell Swift that this is not an AnyObject but rather an Array of some sort (here, an array of String).
There is then a second problem, which is that dict["participants"] is not in fact even an AnyObject - it is an Optional wrapping an AnyObject. So you will have to unwrap it and cast it in order to subscript it.
There is then a third problem, which is that you can't mutate an array value inside a dictionary in place. You will have to extract the value, mutate it, and then replace it.
So, your entire code will look like this:
var dict = [String:AnyObject]()
dict["participants"] = ["foo", "bar"]
var arr = dict["participants"] as [String] // unwrap the optional and cast
arr[0] = "baz" // now we can subscript!
dict["participants"] = arr // but now we have to write back into the dict
Extra for experts: If you want to be disgustingly cool and Swifty (and who doesn't??), you can perform the mutation and the assignment in one move by using a define-and-call anonymous function, like this:
var dict = [String:AnyObject]()
dict["participants"] = ["foo", "bar"]
dict["participants"] = {
var arr = dict["participants"] as [String]
arr[0] = "baz"
return arr
}()
I have NSDictionary, I know it only has one key and one value, how can I directly get the first value from it?
thanks,
If you have a Swift Dictionary and you know you have exactly 1 key/value pair you can do this:
var dict = ["aaa":"bbb"]
let v = dict.values.first!
If you have more than 1 key/value pair then there is no "first" value since dictionaries are unordered. If you have no key/value pairs this will crash.
If you have an NSDictionary, you can use allValues.first!, but you'll have to cast the result because the value will be an AnyObject:
var dict:NSDictionary = ["aaa":"bbb"]
let v = dict.allValues.first! as! String
or:
let v = dict.allValues[0] as! String
Cast to a Swift Dictionary if it isn't one already. Then use the values property, cast to an Array, and get index 0.
let v = Array(myDictionary.values)[0]