I want to create a dictionary out of an array and assign a new custom object to each of them. I'll do stuff with the objects later. How can I do this?
var cals = [1,2,3]
// I want to create out of this the following dictionary
// [1:ReminderList() object, 2:ReminderList() object, 3:ReminderList() object]
let calendarsHashedToReminders = cals.map { ($0, ReminderList()) } // Creating a tuple works!
let calendarsHashedToReminders = cals.map { $0: ReminderList() } // ERROR: "Consecutive statements on a line must be separated by ';'"
map() returns an Array so you'll either have to use reduce() or create the dictionary like this:
var calendars: [Int: ReminderList] = [:]
cals.forEach { calendars[$0] = ReminderList() }
You can also use reduce() to get a oneliner but I'm not a fan of using reduce() to create an Array or a Dictionary.
Related
I want to initialize every time a struct with dictionaries. Later, I'm going to use its properties instead a dictionary's keys and values - it seems rather easier. However, when I try the code below, it tells me that "Return from initializer without initializing all stored properties" and "1. 'self.one' not initialized" and "2. 'self.two' not initialized". My question is how to initialize a struct from a dictionary, so that I have basically a struct with the contents of the dictionary? Or how to transform it into struct?
struct Blabla {
var one: String
var two: [Int]
init(three: [String: [Int]]) {
for i in three {
self.one = i.key
self.two = i.value
}
} ERROR! - Return from initializer without initializing all stored properties
}
struct Blabla {
var one: String
var two: [Int]
init(three: [String: [Int]]) {
one = ""
two = []
for i in three {
self.one = i.key
self.two = i.value
}
} ERROR! - Return from initializer without initializing all stored properties
}
for in clause may have zero runs, in which case struct properties will not be initialized. You have to provide default values (or emit fatalError if you really need to).
While I think your example is pure synthetical, there is no need to loop through array, you can set properties to its last entry.
The issues is that if three is an empty Dictionary, the instance properties one and two don't get initialised. Also, you are overwriting the properties in each iteration of the for loop and the compiler cannot guarantee that there will be any iterations of the loop in compile-time, hence the compiler error.
You could make the initialiser failable to account for this by checking that the dictionary actually contains at least one key-value pair and assigning that first key-value pair to your properties.
struct Blabla {
var one: String
var two: [Int]
init?(three: [String: [Int]]) {
guard let key = three.keys.first, let value = three[key] else { return nil }
one = key
two = value
}
}
However, you should rethink what it is that you are actually trying to achieve, since with your current setup you have a mismatch between your init input values and the properties of your struct.
This code should compile, but it feels unsafe to me to initialize a Struct in this way because:
It assume your dictionary has values in it.
Your stored properties will always have the last value you looped through.
In order to pull values out to satisfy the compiler you need to force unwrap them. (With Dávid Pásztor's guard-letting approach, this can be avoided)
struct Blabla {
var one: String
var two: [Int]
init(three: [String: [Int]]) {
self.one = three.keys.first!
self.two = three[three.keys.first!]!
}
}
let input = ["pizza": [1,2]]
let l = Blabla(three: input)
If I were you I would let the memberwise initializer that you get for free do its thing and provide either a specialized initializer to handle your case of taking a Dictionary as input or move that parsing to another function/class/etc....
The compiler error is clear: If the dictionary is empty the struct members are never initialized. But the code makes no sense anyway as each iteration of the dictionary overwrites the values.
Maybe you mean to map the dictionary to an array of the struct
struct Blabla {
let one: String
let two: [Int]
}
let three = ["A":[1,2], "B":[3,4]]
let blabla = three.map{Blabla(one: $0.key, two: $0.value)}
print(blabla) // [Blabla(one: "A", two: [1, 2]), Blabla(one: "B", two: [3, 4])]
struct blabla{
var a : string
var b : [int] = []
init(_ data: [string:[int]]){
// whatever you want to do
}
}
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 }
So the issue I'm having is that I have an object with a argument in the init() that requires an [UInt8]. I want to be able to grab a range from another array and use that in the init. See example.
class Test {
init(fromArray: [UInt8]) {
// performs work
}
}
let myStockArray: [UInt8] = [1,2,3,4,5,6,7,8] // reference array
let test = Test(fromArray: myStockArray[1...4]) // doesn't work
How can I get this to work? The error I get is: Cannot subscript a value of type '[UInt8]' with an index of type 'CountableClosedRange'
Subscripting an array with a range doesn't return an array and this is the main issue. You are trying to setArraySlice<UInt8> type data to the constructor that have inside [UInt8] type.
Try this approach:
class Test {
init(fromArray: [UInt8]) {
// performs work
}
}
let myStockArray: [UInt8] = [1,2,3,4,5,6,7,8] // reference array
let test = Test(fromArray: Array(myStockArray[1...4]))
I have a JSON that might contain an array of string elements and I want to save it to a variable. So far I did:
import SwiftyJSON
(...)
var myUsers = [""]
if(json["arrayOfUsers"].string != nil)
{
myUsers = json["arrayOfUsers"] //this brings an error
}
The error says:
cannot subscript a value of type JSON with an index of type string
How can I pass this array safely to my variable?
You have to get the array of Strings that SwiftyJSON has prepared when it parsed your JSON data.
I will use if let rather than != nil like you do in your question, and we're going to use SwiftyJSON's .array optional getter:
if let users = json["arrayOfUsers"].array {
myUsers = users
}
If for any reason you get a type error, you can explicitly downcast the SwiftyJSON object itself instead of using the getter:
if let users = json["arrayOfUsers"] as? [String] {
myUsers = users
}
Note that your array of Strings is also not created properly. Do like this:
var myUsers = [String]()
or like hits:
var myUsers: [String] = []
Both versions are equally valid and both create an empty array of strings.
Given that you have an array of optionals:
var values = [AnyObject?]
Can you use a where clause somehow before the optional binding, say, to check for a non-empty array? For example, I know that we can do this:
if !values.isEmpty {
if let value = values[0] {
// ...
}
}
And we can chain a where filter after the optional binding:
// doesn't do you any good when the array is empty
if let value = values[0] where !values.isEmpty {
// ...
}
I'd like to be able evaluate the where first, to prevent an array index out of range error:
// Not valid syntax
if where !values.isEmpty, let value = values[0] {
// ...
}
Is there some form of syntax in Swift 1.2 or 2.x that allows me to express this in a valid manner?
Very simple:
if let value = values.first {
...
}