lets say you have the classes:
class Artwork {
var title = ""
var location =""
var author = ""
}
class GroupedArtworks {
var location = ""
var artworks = [Artworks]()
}
then you have an variable that contains several objects of the class "Artwork":
var arts = [artwork1, artwork2...]
How would I group the objects of the class "Artwork" by "location"?
I would like to end up with another variable containing objects of the class "GroupedArtworks"
and for each object, in the attribute "artworks" have all the objects that have the same "location"
so something like:
var orderedArtworks = [groupedartworks1, groupedartworks2...]
No doubt for loops are involved here.
The solution is super easy with Swift's Dictionary init(grouping:by:)
let artworks: [Artwork] = []
// dictionary type will be [String: [Artwork]]
let dictionary = Dictionary(grouping: artworks, by: \.location)
// now we can easy iterate over (key: String, value: [Artwork]) pairs
let groups: [GroupedArtworks] = dictionary.map { location, artworks in
GroupedArtworks(location: location, artworks: artworks)
}
// or simply
let groups = dictionary.map(GroupedArtworks.init)
// Swift will infer the types of dictionary and the init
but you will need to add this init to your GroupedArtworks
class GroupedArtworks {
let location: String
let artworks: [Artwork]
init(location: String, artworks: [Artwork]) {
self.location = location
self.artworks = artworks
}
}
Documentation
As someone correctly pointed out in the comments, since dicts are unordered collections, your array of GroupedArtworks will be unordered one as-well. But this should not be a problem since you can easily sort it by lets say location.
let groups = dictionary.map(GroupedArtworks.init).sorted(by: \.location)
Related
Based on the following code I would like to be able to create a new ItemList from an existing one. In other words I have an ItemList called First List and I want to create a new ItemList, call it Second List and fill it with the Items from First List.
The way I have it right now is that it creates the Second List as expected, the Items from the First List show in Second List but what doesn't work is when I want to delete only the Items from First List, it deletes Items from both lists. I guess I'm not truly copying the items.
So the question is, how can I copy Items from First List to Second List?
Object Models:
class ItemList: Object {
dynamic var listName = ""
dynamic var createdAt = NSDate()
let items = List<Item>()
}
class Item:Object{
dynamic var productName:String = ""
dynamic var createdAt = NSDate()
}
Code to create Second List from First List
This Works fine, it creates Second List and adds the items from First List but I don't think I'm making copies just showing them in Second List.
let newList = ItemList()
newList.listName = "Second List"
if let selectedList = realm.objects(ItemList.self).filter("listName = %#", "First List").first{
let itemsFromFirstList = selectedList.items
newList.items.append(objectsIn:itemsFromFirstList)
}
try! realm.write {
realm.add(newList)
}
This code is supposed to delete only the items from First List
This actually deletes items from both First List and Second List
let listToDelete = realm.objects(ItemList.self).filter("listName = %#", "First List").first
try! realm.write {
for item in (listToDelete?.items)! {
realm.delete(realm.objects(Item.self).filter("productName = %#", item.productName).first!)
}
}
What you want to do is use:
for record in postsDB.objects(PostModel.self) {
if !combinedDB.objects(PostModel.self).filter("postId == \(record.parentId)").isEmpty {
combinedDB.create(PostModel.self, value: record, update: false)
}
}
The create method is inherited from Object. It tells the target to create a new object. Use true if you want it to look to see if there is already a record there, and update it if there is.
PostModel is the Object type, record is what you want copied.
Edit: I added the if statement to provide more context. You didn't show your class definitions, so I was guessing. This is a working example. I ask for a set of records from DatabaseA and copy it to DatabaseB (postsDB to combinedDB).
So if the type of the object you're trying to insert is a List, I'd recommend you define a subclass of Object, and have at least the list you need as a property.
class TagList: Object {
dynamic var tag = ""
var list = List<PostModel>()
override class func primaryKey() -> String? {
return "tag"
}
}
Full working example illustrating: creating new objects, copying all objects to a second list, deleting from second list after copying, adding to first list (which didn't get anything deleted from it.
import Foundation
import RealmSwift
class Letter: Object {
dynamic var letter = "a"
}
class Letters: Object {
var letterList = List<Letter>()
}
class ListExample {
let listRealmStore = try! Realm() // swiftlint:disable:this force_try
func testThis() {
print(Realm.Configuration.defaultConfiguration.fileURL!)
listRealmStore.beginWrite()
addSingleItems() // add 3 objects to the DB
let firstList = Letters()
let allObjects = listRealmStore.objects(Letter.self)
for item in allObjects {
firstList.letterList.append(item)
}
let secondList = Letters()
let itemsToCopy = firstList.letterList
for item in itemsToCopy {
let obj = listRealmStore.create(Letter.self)
obj.letter = item.letter
secondList.letterList.append(obj)
}
let third = Letter()
third.letter = "Z"
listRealmStore.add(third)
firstList.letterList.append(third)
secondList.letterList.removeLast()
do {
try listRealmStore.commitWrite()
} catch let error {
print("couldn't commit db writes: \(error.localizedDescription)")
}
print("list one:\n\(firstList)")
print("list two:\n\(secondList)")
}
func addSingleItems() {
for letter in ["a", "b", "c"] {
let objectToInsert = Letter()
objectToInsert.letter = letter
listRealmStore.add(objectToInsert)
}
}
}
Results in:
list one:
Letters {
letterList = List<Letter> (
[0] Letter {
letter = a;
},
[1] Letter {
letter = b;
},
[2] Letter {
letter = c;
},
[3] Letter {
letter = Z;
}
);
}
list two:
Letters {
letterList = List<Letter> (
[0] Letter {
letter = a;
},
[1] Letter {
letter = b;
}
);
}
Are you really trying to create copies of your items, or do you just want to be able to remove them from lists independently?
When you do:
newList.items.append(objectsIn: itemsFromFirstList)
you end up with the same objects being in both lists. List<T> just stores references to objects that live within the Realm. Appending an object to a List just references the existing object, it doesn't copy the object.
When you call Realm.delete(_:) you remove that object entirely from the Realm, not just from a single list that it is a member of. To remove an object from a List, you should instead use List.remove(objectAtIndex:).
One part the solution you are looking for could be like this, make copy objects in the list, or you can just use this idea to clone whole list it self:
Previously answered here
As of now, Dec 2020, there is not proper solution of this issue. We have many workarounds though.
Here is the one I have been using, and one with less limitations in my opinion.
Make your Realm Model Object classes conform to codable
class Dog: Object, Codable{
#objc dynamic var breed:String = "JustAnyDog"
}
Create this helper class
class RealmHelper {
//Used to expose generic
static func DetachedCopy<T:Codable>(of object:T) -> T?{
do{
let json = try JSONEncoder().encode(object)
return try JSONDecoder().decode(T.self, from: json)
}
catch let error{
print(error)
return nil
}
}
}
Call this method whenever you need detached / true deep copy of your Realm Object, like this:
//Suppose your Realm managed object: let dog:Dog = RealmDBService.shared.getFirstDog()
guard let detachedDog = RealmHelper.DetachedCopy(of: dog) else{
print("Could not detach Note")
return
}
//Change/mutate object properties as you want
detachedDog.breed = "rottweiler"
As you can see we are piggy backing on Swift's JSONEncoder and JSONDecoder, using power of Codable, making true deep copy no matter how many nested objects are there under our realm object. Just make sure all your Realm Model Classes conform to Codable.
Though its NOT an ideal solution, but its one of the most effective workaround.
I've created a custom class to hold image and its string(its name)
class Countries: NSObject {
var countryName : String
var countryFlag : UIImage
init(countryName: String, countryFlag: UIImage) {
self.countryName = countryName
self.countryFlag = countryFlag
super.init()
}
}
I declared the class
var myList: Array<Countries> = []
And add each country info to the array
let image = UIImage(data:imageData!)
let dd = Countries(countryName: object["CountryName"] as! String, countryFlag: image!)
self.myList.append(dd)
I tried below code to sort the array but doesn't work;
self.myList.sortInPlace({ $0.countryName < $1.countryName })
Does anybody has idea how can I sort my array according to above code?
You can sort an array like this using -sortUsingComparator:, which you pass a block into. The block takes the two objects you want to compare and returns a NSComparisonResult which is your comparison of the two. You could provide a block that uses countryName.
You could alternatively use -sortUsingDescriptors: and pass in a NSSortDescriptor that looks at the countryName field.
I have two separate arrays that I want to import into a dictionary. Order is extremely important because both arrays must match in index
struct MyVariables {
static var users:NSArray!
static var img:NSArray!
}
var data = SearchVC.getData()
MyVariables.users = data.users; //array 1 (key)
MyVariables.img = data.img; //array 2
// Goal is to insert these arrays into a dictionary while maintaing the matching indexes on both arrays
// Dictonary (MyVariables.img, key: MyVariables.users)
A Dictionary does not have a particular order. However, if both arrays have the same length, it is quite easy to iterate over them together:
var dictionary = [NSString: AnyObject]()
for var index = 0; index < data.users.count; index++ {
let img = data.img as! NSString
dictionary[img] = data.users[index]
}
Or, as #robertvojta suggested, use the zip() method:
var dictionary = [NSString: AnyObject]()
for (user, image) in zip(data.users, data.img) {
let img = image as! NSString
dictionary[img] = user
}
The key in a dictionary in swift must be hashable. i.e., not AnyObject.
Assuming you can replace some of your untyped Swift arrays, or cast them like so:
struct MyVariables {
var users:Array<AnyObject>
var img:Array<String>
}
then you can iterate through 1 array using a preferred Swift method and access the second using indexing:
var dictionary = Dictionary<String, AnyObject>()
for (index, element) in enumerate(MyVariables.img) {
dictionary[element] = MyVariables.users[index]
}
Use for loop for travels the array in that as per index access keys and values respective array and add it in dictionary. Its so simple so you can achive your goal using it.
I hope it will help you!
I am trying to create a list to hold the data for a tableview with sections.
I would like to use it like that:
cell.NameLabel.text = list[indexPath.section][indexPath.row].name
Edited
I tried to make the question simple because english is not my main language.
let me try to ask the right question:
I would like to create a dictionary with array of tuples
Something like that:
var myDict = Dictionary<Array<(code: String, type: String)>>()
And I would like to access like that:
myDict["blue"][0].type
The declaration of myDict in your example is wrong, because a Dictionary requires the type of the keys and the type of the values. You should declare it as:
var myDic = Dictionary<String, Array<(code: String, type: String)>>()
Then, you can use it (almost) as you wanted to:
myDic["one"] = [(code: "a", type: "b")]
myDic["two"] = [(code: "c", type: "d"), (code: "e", type: "f")]
let t = myDic["two"]![0].type
...
Note the ! after the myDic["two"]. Thats because accessing a Dictionary by key returns an Optional, you need to unwrap it first.
Actually, this code would be better:
if let item: Array<(code: String, type: String)> = myDic["two"] {
let t = item[0].type
...
}
Well, this would be a very simple Array of Array of an object. I invite you to read the Apple Language Reference of Swift about collections and Arrays :
https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/CollectionTypes.html
import UIKit
class Object {
var name: String
init(string: String) {
name = string
}
}
var objects: [[Object]] = [[Object]]()
for section in 0..<3 {
for i in 0..<10 {
objects[section][i] = Object(string: "My Object \(section) \(i)")
}
}
let myString = objects[2][1].name
I have a Dictionary that holds another Dictionary that holds an Array which holds another Array of a custom class. I'm having a lot of trouble working with these can someone who this comes easy to tell me the ways I can define, initialize, and access and assign to either part specifically.
Dic = [String: [String: [[MyClass]]]]
Sorry if it's confusing.
This code shows you how to do what you asked, but the data structure you requested is quiet cumbersome to use. I'll recommend to think again about what you want to accomplish and review this data structure.
class MyClass {
var name : String
init(name: String) {
self.name = name
}
}
// Create your dictionary
var dic : [String: [String: [[MyClass]]]] = [:]
// Create a list of MyClass object
var list = [MyClass(name: "first"), MyClass(name: "second"), MyClass(name: "third")]
// Create a dictionary with string key and array of array of type MyList
var myClassDic = ["test": [list]]
// update or add new value via the updateValue method
dic.updateValue(myClassDic, forKey: "index1")
// update or add new value via the subscript
dic["index2"] = ["test2": [[MyClass(name: "forth"), MyClass(name: "fith")]]]
// Iterate over your outer dictionairy
for key in dic.keys {
// retrieve an entry from your outer dictionary
var tempDic = dic[key]
// Iterate over your inner dictionary
for sKey in tempDic!.keys {
// retrieve an array of array of MyList Object
var containerList = tempDic![sKey]
// iterate over the outer array
for listVal in containerList! {
//Iterate over the inner array
for sListVal in listVal {
print("\(sListVal.name) ")
}
println()
}
}
}