This is a little hard to explain, but I'll try my best. I am trying to update a Dictionary inside another Dictionary properly. The following code almost does what I need.
var dictionary = Dictionary<String, [Int : Int]>()
func handleStatsValue(tag: Int ) {
let currentValue: Int = dictionary["Score"]?[tag] ?? 0
dictionary["Score"] = [
tag : currentValue + 1
]
}
However, it seems the dictionary is overridden when the tag value changes (e.g. 1 to 2). I need Dictionary to have multiple dictionaries inside of it. Any tips or suggestions are deeply appreciated.
Edit: I'm trying to have multiple dictionaries nested inside a dictionary. It seems whenever the tag value is changed, the dictionary is overridden.
One way to write this would be:
func handleStatsValue(tag: Int) {
dictionary["Score", default: [:]][tag, default: 0] += 1
}
or, written without [_:default:]
func handleStatsValue(tag: Int) {
var scoreDictionary = dictionary["Score"] ?? [:]
scoreDictionary[tag] = (scoreDictionary[tag] ?? 0) + 1
dictionary["Score"] = scoreDictionary
}
However, it's not a good idea to use nested dictionaries to keep your data. Use a custom struct instead and try to avoid tags too:
struct DataModel {
var score: [Int: Int] = [:]
}
I think you need something like this to either increase the value for an existing tag or add a new tag if it doesn't exist
func handleStatsValue(tag: Int ) {
if var innerDict = dictionary["Score"] {
if let value = innerDict[tag] {
innerDict[tag] = value + 1
} else {
innerDict[tag] = 1
}
dictionary["Score"] = innerDict
}
}
Although the code looks a bit strange with the hardcoded key "Score", maybe it would be better to have multiple simple dictionaries instead, like
var score: [Int, Int]()
or if you prefer
var score = Dictionary<Int, Int>()
I've looked through the methods here but I can't quite find what I'm looking for. I'm new-ish to Swift. I would like to extract a subset from a Dictionary based on a Set of key values, preferably without a loop.
For example, if my key Set is of type Set<String> and I have a Dictionary of type Dictionary<String, CustomObject>, I would like to create a new Dictionary of type Dictionary<String, CustomObject> that contains only the key-value pairs associated with the keys in the Set of Strings.
I can see that I could do this with for loop, by initializing a new Dictionary<String, CustomObj>(), checking if the original Dictionary contains a value at each String in the set, and adding key-value pairs to the new Dictionary. I am wondering if there is a more efficient/elegant way to do this however.
I'd be open to finding the subset with an Array of Strings instead of a Set if there is a better way to do it with an Array of keys.
Many thanks!
Swift 5 - You can do this very simply:
let subsetDict = originalDict.filter({ mySet.contains($0.key)})
The result is a new dictionary with the same type as the original but which only contains the key-value pairs corresponding to the keys in mySet.
Your assumption is correct, there is a more concise/swift-ish way to accomplish what you need.
For example you can do it via reduce, a functional programming concept available in Swift:
let subDict = originalDict.reduce([String: CustomObject]()) {
guard mySet.contains($1.key) else { return $0 }
var d = $0
d[$1.key] = $1.value
return d
}
Or, in two steps, first filtering the valid elements, and then constructing back the dictionary with the filtered elements:
let filteredDict = originalDict.filter { mySet.contains($0.key) }
.reduce([CustomObject]()){ var d = $0; d[$1.key]=$1.value; return d }
forEach can also be used to construct the filtered dictionary:
var filteredDict = [CustomObject]()
mySet.forEach { filteredDict[$0] = originalDict[$0] }
, however the result would be good it it would be immutable:
let filteredDict: [String:CustomObject] = {
var result = [String:CustomObject]()
mySet.forEach { filteredDict2[$0] = originalDict[$0] }
return result
}()
Dummy type:
struct CustomObject {
let foo: Int
init(_ foo: Int) { self.foo = foo }
}
In case you'd like to mutate the original dictionary (instead of creating a new one) in an "intersect" manner, based on a given set of keys:
let keySet = Set(["foo", "baz"])
var dict = ["foo": CustomObject(1), "bar": CustomObject(2),
"baz": CustomObject(3), "bax": CustomObject(4)]
Set(dict.keys).subtracting(keySet).forEach { dict.removeValue(forKey: $0) }
print(dict) // ["foo": CustomObject(foo: 1), "baz": CustomObject(foo: 3)]
I'm saving lists in a dictionary. These lists need to be updated. But when searching for an item, I need [] operator. When I save the result to a variable, a copy is used. This can not be used, to change the list itself:
item = dicMyList[key]
if item != nil {
// add it to existing list
dicMyList[key]!.list.append(filename)
// item?.list.append(filename)
}
I know, that I need the uncommented code above, but this accesses and searches again in dictionary. How can I save the result, without searching again? (like the commented line)
I want to speed up the code.
In case you needn't verify whether the inner list was actually existing or not prior to adding element fileName, you could use a more compact solution making use of the nil coalescing operator.
// example setup
var dicMyList = [1: ["foo.sig", "bar.cc"]] // [Int: [String]] dict
var key = 1
var fileName = "baz.h"
// "append" (copy-in/copy-out) 'fileName' to inner array associated
// with 'key'; constructing a new key-value pair in case none exist
dicMyList[key] = (dicMyList[key] ?? []) + [fileName]
print(dicMyList) // [1: ["foo.sig", "bar.cc", "baz.h"]]
// same method used for non-existant key
key = 2
fileName = "bax.swift"
dicMyList[key] = (dicMyList[key] ?? []) + [fileName]
print(dicMyList) // [2: ["bax.swift"], 1: ["foo.sig", "bar.cc", "baz.h"]]
Dictionaries and arrays are value types. So if you change an entry you'll need to save it back into the dictionary.
if var list = dicMyList[key] {
list.append(filename)
dicMyList[key] = list
} else {
dicMyList[key] = [filename]
}
It's a little bit late, but you can do something like this:
extension Optional where Wrapped == Array<String> {
mutating func append(_ element: String) {
if self == nil {
self = [element]
}
else {
self!.append(element)
}
}
}
var dictionary = [String: [String]]()
dictionary["Hola"].append("Chau")
You can try this in the Playground and then adapt to your needs.
In Swift, how can I check if an element exists in an array? Xcode does not have any suggestions for contain, include, or has, and a quick search through the book turned up nothing. Any idea how to check for this? I know that there is a method find that returns the index number, but is there a method that returns a boolean like ruby's #include??
Example of what I need:
var elements = [1,2,3,4,5]
if elements.contains(5) {
//do something
}
Swift 2, 3, 4, 5:
let elements = [1, 2, 3, 4, 5]
if elements.contains(5) {
print("yes")
}
contains() is a protocol extension method of SequenceType (for sequences of Equatable elements) and not a global method as in
earlier releases.
Remarks:
This contains() method requires that the sequence elements
adopt the Equatable protocol, compare e.g. Andrews's answer.
If the sequence elements are instances of a NSObject subclass
then you have to override isEqual:, see NSObject subclass in Swift: hash vs hashValue, isEqual vs ==.
There is another – more general – contains() method which does not require the elements to be equatable and takes a predicate as an
argument, see e.g. Shorthand to test if an object exists in an array for Swift?.
Swift older versions:
let elements = [1,2,3,4,5]
if contains(elements, 5) {
println("yes")
}
For those who came here looking for a find and remove an object from an array:
Swift 1
if let index = find(itemList, item) {
itemList.removeAtIndex(index)
}
Swift 2
if let index = itemList.indexOf(item) {
itemList.removeAtIndex(index)
}
Swift 3, 4
if let index = itemList.index(of: item) {
itemList.remove(at: index)
}
Swift 5.2
if let index = itemList.firstIndex(of: item) {
itemList.remove(at: index)
}
Updated for Swift 2+
Note that as of Swift 3 (or even 2), the extension below is no longer necessary as the global contains function has been made into a pair of extension method on Array, which allow you to do either of:
let a = [ 1, 2, 3, 4 ]
a.contains(2) // => true, only usable if Element : Equatable
a.contains { $0 < 1 } // => false
Historical Answer for Swift 1:
Use this extension: (updated to Swift 5.2)
extension Array {
func contains<T>(obj: T) -> Bool where T: Equatable {
return !self.filter({$0 as? T == obj}).isEmpty
}
}
Use as:
array.contains(1)
If you are checking if an instance of a custom class or struct is contained in an array, you'll need to implement the Equatable protocol before you can use .contains(myObject).
For example:
struct Cup: Equatable {
let filled:Bool
}
static func ==(lhs:Cup, rhs:Cup) -> Bool { // Implement Equatable
return lhs.filled == rhs.filled
}
then you can do:
cupArray.contains(myCup)
Tip: The == override should be at the global level, not within your class/struct
I used filter.
let results = elements.filter { el in el == 5 }
if results.count > 0 {
// any matching items are in results
} else {
// not found
}
If you want, you can compress that to
if elements.filter({ el in el == 5 }).count > 0 {
}
Hope that helps.
Update for Swift 2
Hurray for default implementations!
if elements.contains(5) {
// any matching items are in results
} else {
// not found
}
(Swift 3)
Check if an element exists in an array (fulfilling some criteria), and if so, proceed working with the first such element
If the intent is:
To check whether an element exist in an array (/fulfils some boolean criteria, not necessarily equality testing),
And if so, proceed and work with the first such element,
Then an alternative to contains(_:) as blueprinted Sequence is to first(where:) of Sequence:
let elements = [1, 2, 3, 4, 5]
if let firstSuchElement = elements.first(where: { $0 == 4 }) {
print(firstSuchElement) // 4
// ...
}
In this contrived example, its usage might seem silly, but it's very useful if querying arrays of non-fundamental element types for existence of any elements fulfilling some condition. E.g.
struct Person {
let age: Int
let name: String
init(_ age: Int, _ name: String) {
self.age = age
self.name = name
}
}
let persons = [Person(17, "Fred"), Person(16, "Susan"),
Person(19, "Hannah"), Person(18, "Sarah"),
Person(23, "Sam"), Person(18, "Jane")]
if let eligableDriver = persons.first(where: { $0.age >= 18 }) {
print("\(eligableDriver.name) can possibly drive the rental car in Sweden.")
// ...
} // Hannah can possibly drive the rental car in Sweden.
let daniel = Person(18, "Daniel")
if let sameAgeAsDaniel = persons.first(where: { $0.age == daniel.age }) {
print("\(sameAgeAsDaniel.name) is the same age as \(daniel.name).")
// ...
} // Sarah is the same age as Daniel.
Any chained operations using .filter { ... some condition }.first can favourably be replaced with first(where:). The latter shows intent better, and have performance advantages over possible non-lazy appliances of .filter, as these will pass the full array prior to extracting the (possible) first element passing the filter.
Check if an element exists in an array (fulfilling some criteria), and if so, remove the first such element
A comment below queries:
How can I remove the firstSuchElement from the array?
A similar use case to the one above is to remove the first element that fulfils a given predicate. To do so, the index(where:) method of Collection (which is readily available to array collection) may be used to find the index of the first element fulfilling the predicate, whereafter the index can be used with the remove(at:) method of Array to (possible; given that it exists) remove that element.
var elements = ["a", "b", "c", "d", "e", "a", "b", "c"]
if let indexOfFirstSuchElement = elements.index(where: { $0 == "c" }) {
elements.remove(at: indexOfFirstSuchElement)
print(elements) // ["a", "b", "d", "e", "a", "b", "c"]
}
Or, if you'd like to remove the element from the array and work with, apply Optional:s map(_:) method to conditionally (for .some(...) return from index(where:)) use the result from index(where:) to remove and capture the removed element from the array (within an optional binding clause).
var elements = ["a", "b", "c", "d", "e", "a", "b", "c"]
if let firstSuchElement = elements.index(where: { $0 == "c" })
.map({ elements.remove(at: $0) }) {
// if we enter here, the first such element have now been
// remove from the array
print(elements) // ["a", "b", "d", "e", "a", "b", "c"]
// and we may work with it
print(firstSuchElement) // c
}
Note that in the contrived example above the array members are simple value types (String instances), so using a predicate to find a given member is somewhat over-kill, as we might simply test for equality using the simpler index(of:) method as shown in #DogCoffee's answer. If applying the find-and-remove approach above to the Person example, however, using index(where:) with a predicate is appropriate (since we no longer test for equality but for fulfilling a supplied predicate).
An array that contains a property that equals to
yourArray.contains(where: {$0.propertyToCheck == value })
Returns boolean.
The simplest way to accomplish this is to use filter on the array.
let result = elements.filter { $0==5 }
result will have the found element if it exists and will be empty if the element does not exist. So simply checking if result is empty will tell you whether the element exists in the array. I would use the following:
if result.isEmpty {
// element does not exist in array
} else {
// element exists
}
Swift 4/5
Another way to achieve this is with the filter function
var elements = [1,2,3,4,5]
if let object = elements.filter({ $0 == 5 }).first {
print("found")
} else {
print("not found")
}
As of Swift 2.1 NSArrays have containsObjectthat can be used like so:
if myArray.containsObject(objectImCheckingFor){
//myArray has the objectImCheckingFor
}
Array
let elements = [1, 2, 3, 4, 5, 5]
Check elements presence
elements.contains(5) // true
Get elements index
elements.firstIndex(of: 5) // 4
elements.firstIndex(of: 10) // nil
Get element count
let results = elements.filter { element in element == 5 }
results.count // 2
Just in case anybody is trying to find if an indexPath is among the selected ones (like in a UICollectionView or UITableView cellForItemAtIndexPath functions):
var isSelectedItem = false
if let selectedIndexPaths = collectionView.indexPathsForSelectedItems() as? [NSIndexPath]{
if contains(selectedIndexPaths, indexPath) {
isSelectedItem = true
}
}
if user find particular array elements then use below code same as integer value.
var arrelemnts = ["sachin", "test", "test1", "test3"]
if arrelemnts.contains("test"){
print("found") }else{
print("not found") }
Here is my little extension I just wrote to check if my delegate array contains a delegate object or not (Swift 2). :) It Also works with value types like a charm.
extension Array
{
func containsObject(object: Any) -> Bool
{
if let anObject: AnyObject = object as? AnyObject
{
for obj in self
{
if let anObj: AnyObject = obj as? AnyObject
{
if anObj === anObject { return true }
}
}
}
return false
}
}
If you have an idea how to optimize this code, than just let me know.
Swift
If you are not using object then you can user this code for contains.
let elements = [ 10, 20, 30, 40, 50]
if elements.contains(50) {
print("true")
}
If you are using NSObject Class in swift. This variables is according to my requirement. you can modify for your requirement.
var cliectScreenList = [ATModelLeadInfo]()
var cliectScreenSelectedObject: ATModelLeadInfo!
This is for a same data type.
{ $0.user_id == cliectScreenSelectedObject.user_id }
If you want to AnyObject type.
{ "\($0.user_id)" == "\(cliectScreenSelectedObject.user_id)" }
Full condition
if cliectScreenSelected.contains( { $0.user_id == cliectScreenSelectedObject.user_id } ) == false {
cliectScreenSelected.append(cliectScreenSelectedObject)
print("Object Added")
} else {
print("Object already exists")
}
what about using a hash table for the job, like this?
first, creating a "hash map" generic function, extending the Sequence protocol.
extension Sequence where Element: Hashable {
func hashMap() -> [Element: Int] {
var dict: [Element: Int] = [:]
for (i, value) in self.enumerated() {
dict[value] = i
}
return dict
}
}
This extension will work as long as the items in the array conform to Hashable, like integers or strings, here is the usage...
let numbers = Array(0...50)
let hashMappedNumbers = numbers.hashMap()
let numToDetect = 35
let indexOfnumToDetect = hashMappedNumbers[numToDetect] // returns the index of the item and if all the elements in the array are different, it will work to get the index of the object!
print(indexOfnumToDetect) // prints 35
But for now, let's just focus in check if the element is in the array.
let numExists = indexOfnumToDetect != nil // if the key does not exist
means the number is not contained in the collection.
print(numExists) // prints true
Swift 4.2 +
You can easily verify your instance is an array or not by the following function.
func verifyIsObjectOfAnArray<T>(_ object: T) -> Bool {
if let _ = object as? [T] {
return true
}
return false
}
Even you can access it as follows. You will receive nil if the object wouldn't be an array.
func verifyIsObjectOfAnArray<T>(_ object: T) -> [T]? {
if let array = object as? [T] {
return array
}
return nil
}
You can add an extension for Array as such:
extension Array {
func contains<T>(_ object: T) -> Bool where T: Equatable {
!self.filter {$0 as? T == object }.isEmpty
}
}
This can be used as:
if myArray.contains(myItem) {
// code here
}
May I know how to remove the duplicate data which all the data is passing from the Parse database. I just select one column and pass that column data to this picker view.
I've try to find the query.wherekey but it didn't have the DISTINCT function which similar to the SQL statement, so what should I do to avoid the data duplication?
As you add items one by one into your self.pickerString array, just verify if this array contains or not the new value before addObject new value to the array. For example:
if !self.pickerString.contains(object["Intake"] as! String) {
self.pickerString.append(object["Intake"] as! String)
}
There is no built-in function to remove duplicate items in an array in swift (correct me if I'm wrong). However, you can add new features for array with 'extension' keyword:
extension Array {
func distinct<T: Equatable>() -> [T] {
var newArray = [T]()
for item in self {
if !contains(newArray, item as! T) {
newArray.append(item as! T)
}
}
return newArray
}
}
usage:
let s = ["344","333","1","2","333"]
var p = s.distinct() as [String]
I don't think you have anything like distinct on Parse, you'll have to download all rows and then filter out equal values.
For a functional approach:
func distinct<T: Equatable>(source: [T]) -> [T] {
var unique = [T]()
for item in source {
if !contains(unique, item) {
unique.append(item)
}
}
return unique
}
[...]
self.pickerString = distinct(objects)
[...]