I'm just starting up with RealmSwift, and I'm trying to store an array of Strings in Realm. It doesn't work, so now I'm using List<String>() as an alternative. However, how do I convert these Realm Lists back to [String] again? And if I can't do that, are there any alternatives?
Thanks
However, how do I convert these Realm Lists back to [String] again
You can simply cast List to Array, because List has Sequence Support:
let list = List<String>()
let array = Array(list)
Bear in mind that by converting to an array you'll lose the 'dynamic' quality of a Realm collection (i.e. you'll receive a static array, whereas keeping the original List will provide automatic updating should the source change). But you can create an array by using an extension, e.g.:-
extension RealmCollection
{
func toArray<T>() ->[T]
{
return self.compactMap{$0 as? T}
}
}
Then use:-
let stringList = object.strings.toArray()
Where object is the realm object, and strings is your field.
Here are the details. how to assign an array in the realm list model.
jim.dogs.append(objectsIn: someDogs)
Suppose I have an array, for example:
var myArray = ["Steve", "Bill", "Linus", "Bret"]
And later I want to push/append an element to the end of said array, to get:
["Steve", "Bill", "Linus", "Bret", "Tim"]
What method should I use?
And what about the case where I want to add an element to the front of the array? Is there a constant time unshift?
As of Swift 3 / 4 / 5, this is done as follows.
To add a new element to the end of an Array.
anArray.append("This String")
To append a different Array to the end of your Array.
anArray += ["Moar", "Strings"]
anArray.append(contentsOf: ["Moar", "Strings"])
To insert a new element into your Array.
anArray.insert("This String", at: 0)
To insert the contents of a different Array into your Array.
anArray.insert(contentsOf: ["Moar", "Strings"], at: 0)
More information can be found in the "Collection Types" chapter of "The Swift Programming Language", starting on page 110.
You can also pass in a variable and/or object if you wanted to.
var str1:String = "John"
var str2:String = "Bob"
var myArray = ["Steve", "Bill", "Linus", "Bret"]
//add to the end of the array with append
myArray.append(str1)
myArray.append(str2)
To add them to the front:
//use 'insert' instead of append
myArray.insert(str1, atIndex:0)
myArray.insert(str2, atIndex:0)
//Swift 3
myArray.insert(str1, at: 0)
myArray.insert(str2, at: 0)
As others have already stated, you can no longer use '+=' as of xCode 6.1
To add to the end, use the += operator:
myArray += ["Craig"]
myArray += ["Jony", "Eddy"]
That operator is generally equivalent to the append(contentsOf:) method. (And in really old Swift versions, could append single elements, not just other collections of the same element type.)
There's also insert(_:at:) for inserting at any index.
If, say, you'd like a convenience function for inserting at the beginning, you could add it to the Array class with an extension.
Use += and + operators :
extension Array {
}
func += <V> (inout left: [V], right: V) {
left.append(right)
}
func + <V>(left: Array<V>, right: V) -> Array<V>
{
var map = Array<V>()
for (v) in left {
map.append(v)
}
map.append(right)
return map
}
then use :
var list = [AnyObject]()
list += "hello"
list += ["hello", "world!"]
var list2 = list + "anything"
Here is a small extension if you wish to insert at the beginning of the array without loosing the item at the first position
extension Array{
mutating func appendAtBeginning(newItem : Element){
let copy = self
self = []
self.append(newItem)
self.appendContentsOf(copy)
}
}
In Swift 4.1 and Xcode 9.4.1
We can add objects to Array basically in Two ways
let stringOne = "One"
let strigTwo = "Two"
let stringThree = "Three"
var array:[String] = []//If your array is string type
Type 1)
//To append elements at the end
array.append(stringOne)
array.append(stringThree)
Type 2)
//To add elements at specific index
array.insert(strigTwo, at: 1)
If you want to add two arrays
var array1 = [1,2,3,4,5]
let array2 = [6,7,8,9]
let array3 = array1+array2
print(array3)
array1.append(contentsOf: array2)
print(array1)
Use Deque instead of Array
The main benefit of Deque over Array is that it supports efficient insertions and removals at both ends.
https://swift.org/blog/swift-collections/
var names:Deque = ["Steve", "Bill", "Linus", "Bret"]
Add 'Tim' at the end of names
names.append("Tim")
Add 'Tim' at the begining of names
names.prepend("John")
Remove the first element of names
names.popFirst() // "John"
Remove the last element of names
names.popLast() // "Tim"
From page 143 of The Swift Programming Language:
You can add a new item to the end of an array by calling the array’s append method
Alternatively, add a new item to the end of an array with the addition assignment operator (+=)
Excerpt From: Apple Inc. “The Swift Programming Language.” iBooks. https://itun.es/us/jEUH0.l
To add to the solutions suggesting append, it's useful to know that this is an amortised constant time operation in many cases:
Complexity: Amortized O(1) unless self's storage is shared with another live array; O(count) if self does not wrap a bridged NSArray; otherwise the efficiency is unspecified.
I'm looking for a cons like operator for Swift. It should return a new immutable array with the element tacked on the end, in constant time, without changing the original array. I've not yet found a standard function that does this. I'll try to remember to report back if I find one!
You could use
Myarray.insert("Data #\(index)", atIndex: index)
If you want to append unique object, you can expand Array struct
extension Array where Element: Equatable {
mutating func appendUniqueObject(object: Generator.Element) {
if contains(object) == false {
append(object)
}
}
}
If the array is NSArray you can use the adding function to add any object at the end of the array, like this:
Swift 4.2
var myArray: NSArray = []
let firstElement: String = "First element"
let secondElement: String = "Second element"
// Process to add the elements to the array
myArray.adding(firstElement)
myArray.adding(secondElement)
Result:
print(myArray)
// ["First element", "Second element"]
That is a very simple way, regards!
In Swift 4.2:
You can use
myArray.append("Tim") //To add "Tim" into array
or
myArray.insert("Tim", at: 0) //Change 0 with specific location
Example: students = ["Ben" , "Ivy" , "Jordell"]
1) To add single elements to the end of an array, use the append(_:)
students.append(\ "Maxime" )
2) Add multiple elements at the same time by passing another array or a sequence of any kind to the append(contentsOf:) method
students.append(contentsOf: ["Shakia" , "William"])
3) To add new elements in the middle of an array by using the insert(_:at:) method for single elements
students.insert("Liam" , at:2 )
4) Using insert(contentsOf:at:) to insert multiple elements from another collection or array literal
students.insert(['Tim','TIM' at: 2 )
Swift 5.3, I believe.
The normal array wasvar myArray = ["Steve", "Bill", "Linus", "Bret"]
and you want to add "Tim" to the array, then you can use myArray.insert("Tim", at=*index*)so if you want to add it at the back of the array, then you can use myArray.append("Tim", at: 3)
okay, i'm trying to have the user add a key and value pair to a dictionary i created and have it show up in a table view. i do that just fine but i cant seem to figure out how to add another pair. when i go to add another it replaces the last one. id really like to have multiple pairs. can someone help please?
heres my code:
//declaring the dictionary
var cart = [String:String]()
//attempting to add to dictionary
cart[pizzaNameLabel.text!] = formatter.stringFromNumber(total)
This is how dictionary works:
In computer science, an associative array, map, symbol table, or
dictionary is an abstract data type composed of a collection of (key,
value) pairs, such that each possible key appears at most once in the
collection.
So
var cart = [String:String]()
cart["key"] = "one"
cart["key"] = "two"
print(cart)
will print only "key" - "two" part. It seems that you may need an array of tuples instead:
var cart = [(String, String)]()
cart.append(("key", "one"))
cart.append(("key", "two"))
print(cart)
will print both pairs.
From Swift 5.0, you can use KeyValuePairs like ordered dictionary type with multiple keys.
See this Apple Document of KeyValuePairs. ;)
let recordTimes: KeyValuePairs = ["Florence Griffith-Joyner": 10.49,
"Evelyn Ashford": 10.76,
"Evelyn Ashford": 10.79,
"Marlies Gohr": 10.81]
print(recordTimes.first!)
I have a variable set of objects that I need to place in a dictionary. I'm trying to add them to the dictionary in a for loop but from what I'm understanding dictionaries are immutable so they need to be declared immediately. How do I create a dictionary list of items that are not predetermined?
var newItems = [:]
for item in self.items{
newItems["\(item.key)"]["name"] = "A new item"
}
does not use the second value
var newItems : [String:String] = [:]
for i in 1..10{
newItems[i.description] = "A new item"
}
for more information https://www.weheartswift.com/dictionaries/
The problem with your original code is that dictionaries only have one key, so this construct newItems["\(item.key)"]["name"] is syntactically incorrect. If you had a fixed number of properties you could use a struct and put that in a dictionary. As you posed the question, though, you need to create a dictionary where the stored elements themselves are dictionaries. So, although I didn't actually put this into Xcode, it's a template for what you need to do:
var newItems = [:[:]]()
for item in self.items {
var itemDict = [:]()
for prop in whereeveryourpropertiescomefrom {
itemDict[prop] = valueforthisproperty
}
newItems["\(item.key)"] = itemDict
}
Of course, if your properties were initially stored in a dictionary unique to this item (equivalent of the inner loop), just store it directly into newItems.
Then, you could reference things as
let value = newItems["\(item.key)"]?.["property key"]
Notice the dictionary retrieval returns an optional you have to deal with.
The solution was when initializing the dictionary to create another dictionary
var newItems: [String:[String:AnyObject]]()
With the original swift I could turn an NSSet (e.g. of Strings) into a typed array with the following syntax:
var stringArray = exampleSet.allObjects as [String]
With the new update I am getting the above error. What is the best way now to convert the Set into an array?
It looks as if your exampleSet is not an NSSet but a native
Swift Set which was introduced with Swift 1.2 (compare https://stackoverflow.com/a/28426765/1187415).
In that case you can convert it to an array simply with
let array = Array(exampleSet)
Looks like 'set' is a keyword. Try using a different variable name