I am trying to use filter on an array, but I keep getting this error. I checked the earlier answer, but I have already implemented "equatable" on my object.
Btw, what does this error mean anyway?
// trying to use filter
var distance_array = [
FilterOption(title: "0.5 miles", value:500, currentSetting: false)...]
var filtered_distance: [FilterOption]!
filtered_distance = distance_array.filter({ ($0.currentValue == true) })
// FilterOption Class
class FilterOption: NSObject, Equatable {
var title:String!
var value: AnyObject?
var currentSetting: Bool!
init(title:String, value:AnyObject?, currentSetting:Bool){
self.title = title
self.value = value
self.currentSetting = currentSetting
}
class func convertDictionaryToFilterOption(dict:Dictionary<String, String>) -> FilterOption{
return FilterOption(title:dict["name"]!, value:dict["code"]!, currentSetting: false)
}
}
func == (lhs: FilterOption, rhs: FilterOption) -> Bool {
var title = (lhs.title == rhs.title)
var setting = (lhs.currentSetting! == rhs.currentSetting!)
return title && setting
}
That compiler error is a little misleading. If you were really testing to see if one FilterOption was equal to another (a common problem that rears its head when comparing objects in filter closure), then you'd have to make it conform to Equatable. But that's not the problem here.
In this case the problem is simply that the code refers to currentValue, rather than currentSetting. If you fix that, the compiler error goes away.
By the way, you can simplify that filter statement:
let filteredDistance = distanceArray.filter { $0.currentSetting }
The currentSetting is already a Bool, so if you're testing to see if it's true, you can just return it directly. There were also some extraneous parentheses.
Related
I have this class
class InboxInterests {
var title = ""
var eventID = 0
var count = ""
var added = 0
init(title : String, eventID : NSInteger, count: String, added : NSInteger) {
self.title = title
self.eventID = eventID
self.count = count
self.added = added
}
}
And i use it like this
var array: [InboxInterests] = [InboxInterests]()
Add item
let post = InboxInterests(title: "test",eventID : 1, count: "test", added: 0)
self.array.append(post)
I want to find the index by eventID key and change the value of added key in the same index
How is that possible?
For me, the above answer did not work. So, what I did was first find the index of the object that I want to replace then using the index replace it with the new value
if let row = self.upcoming.index(where: {$0.eventID == id}) {
array[row] = newValue
}
In Swift 5.0:
if let row = self.upcoming.firstIndex(where: {$0.eventID == id}) {
array[row] = newValue
}
Since you are using a class, use filter and first to find the value:
array.filter({$0.eventID == id}).first?.added = value
In this you:
filter the array down to elements that match the event ID
pick the first result, if any
then set the value
This works since classes are pass by reference. When you edit the return value from array.filter({$0.eventID == id}).first?, you edit the underlying value. You'll need to see the answers below if you are using a struct
EDIT: In Swift 3 you can save yourself a couple of characters
array.first({$0.eventID == id})?.added = value
EDIT: Swift 4.2:
array.first(where: { $0.eventID == id })?.added = value
array.filter {$0.eventID == id}.first?.added = value
The filter operator is not the best in this case, it works for some of you because classes are passed by reference.
Explanation: (You can copy the following code in a playground if you want to verify it).
class Book {
let id: Int
var title = "default"
init (id: Int) {
self.id = id
}
}
var arrayBook = [Book]()
arrayBook.append(Book(id: 0))
arrayBook.append(Book(id:1))
arrayBook.forEach { book in
print(book.title)
}
arrayBook.filter{ $0.id == 1 }.first?.title = "modified"
arrayBook.forEach { book in
print(book.title)
}
Arrays are copied by value not reference, so when you are using filter you are creating a new array (different than the initial), but when you modify the new one, the initial one gets modified too because both are pointing to the same class (classed are passed by reference), so after the filter your array will have changed and the new one gets deallocated. So in this case it will print "default", "default" and then "default, "modified".
What happens if you change class for struct, the value will be passed by value not reference so you will have 2 arrays in memory with different values, so if you go through arrayBooks again it will print before the filter "default","default", and then "default", "default" again. Because when you are using the filter you are creating and modifying a new array that will get deallocated if you do not store it).
The solution is using map, creating a new array with all the values but with the modified items or fields that we want and then replace our array with the new one. This will print "default", "default" before the map, and then "default", "modified"
This will work with structs, classes and everything that you want :).
struct Book {
let id: Int
var title = "default"
init (id: Int) {
self.id = id
}
}
var arrayBook = [Book]()
arrayBook.append(Book(id: 0))
arrayBook.append(Book(id:1))
arrayBook.forEach { book in
print(book.title)
}
arrayBook = arrayBook.map{
var mutableBook = $0
if $0.id == 1 {
mutableBook.title = "modified"
}
return mutableBook
}
arrayBook.forEach { book in
print(book.title)
}
array = array.map { $0.eventID == id ? newValue : $0 }
If you conform your class to Equatable then this would work:
extension Array where Element: Equatable {
#discardableResult
public mutating func replace(_ element: Element, with new: Element) -> Bool {
if let f = self.firstIndex(where: { $0 == element}) {
self[f] = new
return true
}
return false
}
}
Use like this:
array.replace(prev, with: new)
I'm using ResearchKit's stepResultForStepIdentifier method successfully for other question types, but can't find correct syntax to pre-populate the results for a TextChoiceQuestion.
Below is an unsuccessful attempt at setting the result for the sample TextChoice question in ORKCatalog. Any advice on correct approach?
func stepResultForStepIdentifier(stepIdentifier: String) -> ORKStepResult? {
var stepResults = [ORKQuestionResult]()
if stepIdentifier == "TextChoiceQuestionStep" {
var questionDefault = ORKChoiceQuestionResult(identifier: stepIdentifier)
questionDefault.choiceAnswers?.append("choice_2")
stepResults.append(questionDefault)
}
var defaults = ORKStepResult(stepIdentifier: stepIdentifier, results: stepResults)
return defaults
}
Is the choiceAnswers array nil? When you do questionDefault.choiceAnswers?.append, choiceAnswers might be nil, so this might do nothing.
Instead do questionDefault.choiceAnswers = ["choice_2"]
Im trying to ask for some values from a variable.
The variable is going to have the description of the weather and i want to ask for specific words in order to show different images (like a sun, rain or so)
The thing is i have code like this:
if self.descriptionWeather.description.rangeOfString("Clear") != nil
{
self.imageWeather.image = self.soleadoImage
}
if self.descriptionWeather.description.rangeOfString("rain") != nil
{
self.imageWeather.image = self.soleadoImage
}
if self.descriptionWeather.description.rangeOfString("broken clouds") != nil
{
self.imageWeather.image = self.nubladoImage
}
Because when i tried to add an "OR" condition xcode gives me some weird errors.
Is it possible to do a swich sentence with that? Or anyone knows how to do add an OR condition to the if clause?
I had a similar problem today and realized this question hasn't been updated since Swift 1! Here's how I solved it in Swift 4:
switch self.descriptionWeather.description {
case let str where str.contains("Clear"):
print("clear")
case let str where str.contains("rain"):
print("rain")
case let str where str.contains("broken clouds"):
print("broken clouds")
default:
break
}
Swift 5 Solution
func weatherImage(for identifier: String) -> UIImage? {
switch identifier {
case _ where identifier.contains("Clear"),
_ where identifier.contains("rain"):
return self.soleadoImage
case _ where identifier.contains("broken clouds"):
return self.nubladoImage
default: return nil
}
}
You can do this with a switch statement using value binding and a where clause. But convert the string to lowercase first!
var desc = "Going to be clear and bright tomorrow"
switch desc.lowercaseString as NSString {
case let x where x.rangeOfString("clear").length != 0:
println("clear")
case let x where x.rangeOfString("cloudy").length != 0:
println("cloudy")
default:
println("no match")
}
// prints "clear"
Swift language has two kinds of OR operators - the bitwise ones | (single vertical line), and the logical ones || (double vertical line). In this situation you need a logical OR:
if self.descriptionWeather.description.rangeOfString("Clear") != nil || self.descriptionWeather.description.rangeOfString("clear") != nil {
self.imageWeather.image = self.soleadoImage
}
Unlike Objective-C where you could get away with a bitwise OR in exchange for getting a slightly different run-time semantic, Swift requires a logical OR in the expression above.
If you do this a lot, you can implement a custom ~= operator that defines sub-string matching. It lends itself to this nice syntax:
switch "abcdefghi".substrings {
case "def": // calls `"def" ~= "abcdefghi".substrings`
print("Found substring: def")
case "some other potential substring":
print("Found \"some other potential substring\"")
default: print("No substring matches found")
}
Implementation:
import Foundation
public struct SubstringMatchSource {
private let wrapped: String
public init(wrapping wrapped: String) {
self.wrapped = wrapped
}
public func contains(_ substring: String) -> Bool {
return self.wrapped.contains(substring)
}
public static func ~= (substring: String, source: SubstringMatchSource) -> Bool {
return source.contains(substring)
}
}
extension String {
var substrings: SubstringMatchSource {
return SubstringMatchSource(wrapping: self)
}
}
I'd recommend using a dictionary instead, as a mapping between the substring you're searching for and the corresponding image:
func image(for weatherString: String) -> UIImage? {
let imageMapping = [
"Clear": self.soleadoImage,
"rain": self.soleadoImage,
"broken clouds": self.nubladoImage]
return imageMapping.first { weatherString.contains($0.key) }?.value
}
A dictionary gives you flexibility, adding new mappings is easy to do.
This link also describes overloading operator ~= which is actually used by the switch statement for matching cases to allow you to match regular expressions.
is there a possibility to get an object from an array with an specific property? Or do i need to loop trough all objects in my array and check if an property is the specific i was looking for?
edit: Thanks for given me into the correct direction, but i have a problem to convert this.
// edit again: A ok, and if there is only one specific result? Is this also a possible method do to that?
let imageUUID = sender.imageUUID
let questionImageObjects = self.formImages[currentSelectedQuestion.qIndex] as [Images]!
// this is working
//var imageObject:Images!
/*
for (index, image) in enumerate(questionImageObjects) {
if(image.imageUUID == imageUUID) {
imageObject = image
}
}
*/
// this is not working - NSArray is not a subtype of Images- so what if there is only 1 possible result?
var imageObject = questionImageObjects.filter( { return $0.imageUUID == imageUUID } )
// this is not working - NSArray is not a subtype of Images- so what if there is only 1 possible result?
You have no way to prove at compile-time that there is only one possible result on an array. What you're actually asking for is the first matching result. The easiest (though not the fastest) is to just take the first element of the result of filter:
let imageObject = questionImageObjects.filter{ $0.imageUUID == imageUUID }.first
imageObject will now be an optional of course, since it's possible that nothing matches.
If searching the whole array is time consuming, of course you can easily create a firstMatching function that will return the (optional) first element matching the closure, but for short arrays this is fine and simple.
As charles notes, in Swift 3 this is built in:
questionImageObjects.first(where: { $0.imageUUID == imageUUID })
Edit 2016-05-05: Swift 3 will include first(where:).
In Swift 2, you can use indexOf to find the index of the first array element that matches a predicate.
let index = questionImageObjects.indexOf({$0.imageUUID == imageUUID})
This is bit faster compared to filter since it will stop after the first match. (Alternatively, you could use a lazy sequence.)
However, it's a bit annoying that you can only get the index and not the object itself. I use the following extension for convenience:
extension CollectionType {
func find(#noescape predicate: (Self.Generator.Element) throws -> Bool) rethrows -> Self.Generator.Element? {
return try indexOf(predicate).map({self[$0]})
}
}
Then the following works:
questionImageObjects.find({$0.imageUUID == imageUUID})
Yes, you can use the filter method which takes a closure where you can set your logical expression.
Example:
struct User {
var firstName: String?
var lastName: String?
}
let users = [User(firstName: "John", lastName: "Doe"), User(firstName: "Bill", lastName: "Clinton"), User(firstName: "John", lastName: "Travolta")];
let johns = users.filter( { return $0.firstName == "John" } )
Note that filter returns an array containing all items satisfying the logical expression.
More info in the Library Reference
Here is a working example in Swift 5
class Point{
var x:Int
var y:Int
init(x:Int, y:Int){
self.x = x
self.y = y
}
}
var p1 = Point(x:1, y:2)
var p2 = Point(x:2, y:3)
var p3 = Point(x:1, y:4)
var points = [p1, p2, p3]
// Find the first object with given property
// In this case, firstMatchingPoint becomes p1
let firstMatchingPoint = points.first{$0.x == 1}
// Find all objects with given property
// In this case, allMatchingPoints becomes [p1, p3]
let allMatchingPoints = points.filter{$0.x == 1}
Reference:
Trailing Closure
Here is other way to fetch particular object by using object property to search an object in array.
if arrayTicketsListing.contains({ $0.status_id == "2" }) {
let ticketStatusObj: TicketsStatusList = arrayTicketsListing[arrayTicketsListing.indexOf({ $0.status_id == "2" })!]
print(ticketStatusObj.status_name)
}
Whereas, my arrayTicketsListing is [TicketsStatusList] contains objects of TicketsStatusList class.
// TicketsStatusList class
class TicketsStatusList {
internal var status_id: String
internal var status_name: String
init(){
status_id = ""
status_name = ""
}
}
I have these two objects in my model:
Message:
class Message: Object {
//Precise UNIX time the message was sent
dynamic var sentTime: NSTimeInterval = NSDate().timeIntervalSince1970
let images = List<Image>()
}
Image:
class Image: Object {
dynamic var mediaURL: String = ""
var messageContainingImage: Message {
return linkingObjects(Message.self, forProperty: "images")[0]
}
}
I want to form a query which returns messages and images, messages sorted by sentTime and images sorted by their messageContainingImage's sent time. They'd be sorted together.
The recommended code for a query is this:
let messages = Realm().objects(Message).sorted("sentTime", ascending: true)
This returns a Result<Message> object. A Result doesn't have a way to be joined to another Result. There are other issues in my way too, such as, if I could combine them, how would I then perform a sort.
Additional thoughts:
I could also add a property to Image called sentTime, then once they're combined I'd be able to call that property on both of them.
I could make them both subclass from a type which has sentTime. The problem is, doing Realm().objects(Message) would only returns things which are messages, and not subclasses of Message.
How would I be able to do this?
My end goal is to display these message and image results in a tableview, messages separately from their attached image.
I think, inheritance is not the right solution here, this introduces more drawbacks by complicating your object schema, than it's worth for your use case.
Let's go back to what you wrote is your end goal: I guess you want to display messages and images together in one table view as separated rows, where the images follow their message. Do I understand that correctly?
You don't need to sort both, sorting the messages and accessing them and their images in a suitable way will ensure that everything is sorted correctly. The main challenge is more how to enumerate / random-access this two-dimensional data structure as an one-dimensional sequence.
Depending on the amount of data, you query, you have to decide, whether you can go a simple approach by keeping them all in memory at once, or introducing a view object on top of Results, which takes care of accessing all objects in order.
The first solution could just look like this:
let messages = Realm().objects(Message).sorted("sentTime", ascending: true)
array = reduce(messages, [Object]()) { (var result, message) in
result.append(message)
result += map(message.images) { $0 }
return result
}
While the latter solution is more complex, but could look like this:
// Let you iterate a list of nodes with their related objects as:
// [a<list: [a1, a2]>, b<list: [b1, b2, b3]>]
// in pre-order like:
// [a, a1, a2, b, b1, b2, b3]
// where listAccessor returns the related objects of a node, e.g.
// listAccessor(a) = [a1, a2]
//
// Usage:
// class Message: Object {
// dynamic var sentTime = NSDate()
// let images = List<Image>()
// }
//
// class Image: Object {
// …
// }
//
// FlattenedResultsView(Realm().objects(Message).sorted("sentTime"), listAccessor: { $0.images })
//
class FlattenedResultsView<T: Object, E: Object> : CollectionType {
typealias Index = Int
typealias Element = Object
let array: Results<T>
let listAccessor: (T) -> (List<E>)
var indexTransformVectors: [(Int, Int?)]
var notificationToken: NotificationToken? = nil
init(_ array: Results<T>, listAccessor: T -> List<E>) {
self.array = array
self.listAccessor = listAccessor
self.indexTransformVectors = FlattenedResultsView.computeTransformVectors(array, listAccessor)
self.notificationToken = Realm().addNotificationBlock { note, realm in
self.recomputeTransformVectors()
}
}
func recomputeTransformVectors() {
self.indexTransformVectors = FlattenedResultsView.computeTransformVectors(array, listAccessor)
}
static func computeTransformVectors(array: Results<T>, _ listAccessor: T -> List<E>) -> [(Int, Int?)] {
let initial = (endIndex: 0, array: [(Int, Int?)]())
return reduce(array, initial) { (result, element) in
var array = result.array
let list = listAccessor(element)
let vector: (Int, Int?) = (result.endIndex, nil)
array.append(vector)
for i in 0..<list.count {
let vector = (result.endIndex, Optional(i))
array.append(vector)
}
return (endIndex: result.endIndex + 1, array: array)
}.array
}
var startIndex: Index {
return indexTransformVectors.startIndex
}
var endIndex: Index {
return indexTransformVectors.endIndex
}
var count: Int {
return indexTransformVectors.count
}
subscript (position: Index) -> Object {
let vector = indexTransformVectors[position]
switch vector {
case (let i, .None):
return array[i]
case (let i, .Some(let j)):
return listAccessor(array[i])[j]
}
}
func generate() -> GeneratorOf<Object> {
var arrayGenerator = self.array.generate()
var lastObject: T? = arrayGenerator.next()
var listGenerator: GeneratorOf<E>? = nil
return GeneratorOf<Object> {
if listGenerator != nil {
let current = listGenerator!.next()
if current != nil {
return current
} else {
// Clear the listGenerator to jump back on next() to the first branch
listGenerator = nil
}
}
if let currentObject = lastObject {
// Get the list of the currentObject and advance the lastObject already, next
// time we're here the listGenerator went out of next elements and we check
// first whether there is anything on first level and start over again.
listGenerator = self.listAccessor(currentObject).generate()
lastObject = arrayGenerator.next()
return currentObject
} else {
return nil
}
}
}
}