Lets say I have dictionaries like below and wanted an array of red dogs. I figured I need to get an array of all the names of the type "dog" using the first dictionary, and then use the name key and the color to search the final dictionary to get ["Polly,"jake"]. I've tried using loops but can't figure out how to iterate through the dictionary.
var pets = ["Polly" : "dog", "Joey" : "goldfish", "Alex" : "goldfish", "jake" : "dog"]
var petcolor = ["Polly" : "red", "Joey" : "black", "Alex" : "yellow", "jake":red"]
The correct solution would seem to be to create a Pet struct (or class) and collate all of this information into a struct and build either an array or dictionary full of these values.
struct Pet {
let name: String
let type: String
let color: String
init(name: String, type: String, color: String) {
self.name = name
self.type = type
self.color = color
}
}
Now, let's build an array of these pets:
var goodPets = [Pet]()
for (petName, petType) in pets {
guard let petColor = petcolor[petName] else {
// Found this pet's type, but couldn't find its color. Can't add it.
continue
}
goodPets.append(Pet(name: petName, type: petType, color: petColor))
}
Now that we've filled out goodPets, pulling out any particular subset of Pets becomes very easy:
let redDogs = goodPets.filter { $0.type == "dog" && $0.color = "red" }
And although this answer looks like a lot of set up & legwork compared to other answers, the major advantage here is that once we build the goodPets array, any way we want to scoop pets out of there ends up being more efficient. And as we increase the number of properties the pets have, this becomes more and more true compared to the other answers.
If you'd rather store our model objects in a dictionary continuing to use the names as the keys, we can do that as well, but the filter looks a little bit stranger.
Building the dictionary looks mostly the same:
var goodPets = [String : Pet]()
for (petName, petType) in pets {
guard let petColor = petcolor[petName] else {
// Found this pet's type, but couldn't find its color. Can't add it.
continue
}
goodPets[petName] = (Pet(name: petName, type: petType, color: petColor))
}
But the filter is slightly different:
let redDogs = goodPets.filter { $0.1.type = "dog" && $0.1.color = "red" }
Note that in both cases, redDogs has the type [Pet], that is, an array of Pet values.
You can iterate through a dictionary like this:
for key in pets.keys() {
if pets[key] == "Dog" {
}
}
Or:
for (name, pet) in pets {
if pet == "Dog" {
}
}
nhgrif is probably correct about structure but, to answer the literal question:
let dogs = Set(pets.filter { $0.1 == "dog" }.map { $0.0 })
let redAnimals = Set(petscolor.filter { $0.1 == "red" }.map { $0.0 })
let redDogs = dogs.intersect(redAnimals)
Each filter is a block that operates on a (key, value) tuple, testing the value and ultimately creating a dictionary with only the matching (key, value) pairs. Each map then converts that filtered dictionary into an array by discarding the values and just keeping the keys.
Each array is turned into a set to support the intersect operation. The intersect then determines the intersection of the two results.
Related
i have json objects like and parsed in an array
let objects = [Object]()
struct Object {
name: String
id: Int
}
Suppose like
let objects [Object(name:oscar, id: 11), Object(name:sanchez, id: 12),Object(name:emily, id: 15),Object(name:clarck, id: 31) ... ]
How can i take the string array as below also with this name which object belongs to ? ( so i can use object easily)
let stringPropertyArray = [oscar, sanchez,emily,clarck ... ]
Thanks
how i will find the object ? if you have "emily" and i want to item.id which emily belongs to ?
Perhaps you want something like
if let ob = objects.first {$0.name == "emily"} {
print(ob.id)
}
But if your goal is to search quickly, it would be better to have a dictionary keyed by the value you will be searching on.
I think this is what you want
let stringPropertyArray: [String] = objects.map {$0.name}
There are 2 approaches you can use:
by looping (traditional approach)
var listName: [String] = []
for item in objects {
listName.append(item.name)
}
by using higher order function
let listName = objects.map{ $0.name }
There would be a case if your name property is optional and for some object, name property value is nil then we should use compactMap higher order function in order to avoid nil object in the list
let listName = objects.compactMap{ $0.name }
To find any specific object we can use filter like below:
let object = objects.filter{
$0.name == "sanchez" }.first
// OR
let object = objects.first { object -> Bool in
object.name == "emily" }
I have two dictionaries in Swift with few similar values which are in dynamic mode:
dict1 = ["a1":"value 1", "b1":"value2", "c1":"value 3"]
dict2 = ["b1": "value2", "d1": "value4"]
If I want to compare these two dictionaries and want to extract only the matching keys even nested, how do I about to do that?
If you want the common keys with the value in one of them :
let intersectionDict = dict1.filter { dict2.keys.contains($0.key) }
//Or
let intersectionDict2 = dict2.filter { dict1.keys.contains($0.key) }
If you want the values to match too:
let intersectionDict3 = dict1.filter { dict2[$0.key] == $0.value }
And the result is:
print(intersectionDict3) //["b1": "value2"]
As others have shown, you can do this using a filter statement. You can make it even quicker by always filtering the smaller of the two dicts, improving the time complexity from O(dict1.size) to O(min(dict1.size, dict2.size).
extension Dictionary {
func intersectingByKeys(with other: Dictionary) -> Dictionary {
let (smallerDict, largerDict) = (self.count < other.count) ? (self, other) : (other, self)
return smallerDict.filter { key, _ in largerDict.keys.contains(key) }
}
}
let dict1 = ["a1":"value 1", "b1":"value2", "c1":"value 3"]
let dict2 = ["b1": "value2", "d1": "value4"]
print(dict1.intersectingByKeys(with: dict2))
You can create a Set from the keys of one of the dictionaries and call intersection on the Set with the keys of the other dictionary.
let matchingKeys = Set(dict1.keys).intersection(dict2.keys) // {"b1"}
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 have an array of dictionaries with the following type of structure (which is already sorted) :
[
[
"id": 1,
"name": "ItemA",
"url": "http://url.com"
],
[
"id": 32,
"name": "ItemB",
"url": "http://url.com"
],
...
]
Declared as an array of dictionaries for AnyObject :
var arrayApps = [[String:AnyObject]]()
This array of dictionaries is generated using SwiftyJson :
[..]
if let resData = swiftyJsonVar["data"].arrayObject {
self.arrayItems = resData as! [[String:AnyObject]]
}
[..]
My Goal is to display those items in sections by using the sections headers but after trying to figure it out and looking for an answer, i'm unable to move on.
I've tried to groupe the dictionaries by letters to get a result like this:
[
"A":{[foo1],[foo2]},
"D":{[foo3],[foo5]},
"F":{[foo4],[foo6]}
...
]
But no luck, i've always ended up with errors because my array contains "Optionals".
In summary :
How can I generate Alphabetical section headers based on the name inside a TableView using an array of dictionaries not grouped like the one given above in Swift 3 ?
Thank you in advance !!
You can use the .sorted(by: ) method of Array to compare to elements of you array with each other.
This yields a sortedArray:
let sortedArray = arrayOfApps.sorted(by: {($0["name"] as! String) <= ($1["name"] as! String)})
This will crash if the itemName is not a String but I left it to you to handle any errors. For example changing it to:
$0["name"] as? String ?? ""
EDIT:
// Removed examples and added extension to create desired result
I found one of my old projects where I wrote such extension. Changed it a bit to suit your needs, tell me if it needs some change still:
extension Array {
func sectionTitlesForArray(withName name: (Element) -> String) -> Array<(title: String, elements: NSMutableArray)> {
var sectionTitles = Array<(title: String, elements: NSMutableArray)>()
self.forEach({ element in
var appended = false
sectionTitles.forEach({ title, elements in
if title == name(element) {
elements.add(element)
appended = true
}
})
if appended == false {
sectionTitles.append((title: name(element), elements: [element]))
}
})
return sectionTitles
}
}
// Usage single letter as Section title:
let sectionTitles = arrayOfApps.sectionTitlesForArray(withName: {
let name = $0["name"] as! String
return String(name[name.startIndex])
})
// Quick dirty pretty-print:
sectionTitles.forEach({ sectionTitle in
print("Section title: \(sectionTitle.title) \n")
sectionTitle.elements.forEach({ object in
let element = object as! Dictionary<String,Any>
print("Element name: \(element["name"]!)")
})
print("")
})
Given an NSTableView that has an array of structures as its datasource. A user can click on any column heading to sort by that column. The column identifiers match the property names of the properties within the structure.
Given a structure
struct MyStructure {
var col0data = "" //name matches the column identifier
var col1data = ""
}
and an array of structures
var myArray = [MyStructure]()
The goal is that when a column heading is clicked, use that column's identifier to sort the array of structures by that column identifier/property
With an array of dictionaries, it was easy...
self.myArrayOfDictionaries.sortInPlace {
(dictOne, dictTwo) -> Bool in
let d1 = dictOne[colIdentifier]! as String;
let d2 = dictTwo[colIdentifier]! as String;
return d1 < d2 //or return d1 > d2 for reverse sort
}
The question is how to access the properties of the Structure dynamically, something like
let struct = myArray[10] as! MyStructure //get the 10th structure in the array
let value = struct["col0data"] as! String //get the value of the col0data property
If there is a better way, suggestions would be appreciated.
I should also note that the structure may have 50 properties so this is an effort to reduce the amount of code needed to sort the array by any one of those properties.
edit:
One solution is to change the structure to a class derived from NSObject. Then the properties could be accessed via .valueForKey("some key"). However, I am trying to keep this Swifty.
Maybe I have a solution to your problem. The advantage of this code over your solution is here you don't need to add a subscript method to your struct to create an hardcoded String-Property-Value map via code.
Here's my extension
extension _ArrayType {
func sortedBy(propertyName propertyName: String) -> [Self.Generator.Element] {
let mirrors = self.map { Mirror(reflecting: $0) }
let propertyValues = mirrors.map { $0.children.filter { $0.label == propertyName }.first?.value }
let castedValues = propertyValues.map { $0 as? String }
let sortedArray = zip(self, castedValues).sort { (left, right) -> Bool in
return left.1 < right.1
}.map { $0.0 }
return sortedArray
}
}
Usage
struct Animal {
var name: String
var type: String
}
let animals = [
Animal(name: "Jerry", type: "Mouse"),
Animal(name: "Tom", type: "Cat"),
Animal(name: "Sylvester", type: "Cat")
]
animals.sortedBy(propertyName: "name")
// [{name "Jerry", type "Mouse"}, {name "Sylvester", type "Cat"}, {name "Tom", type "Cat"}]
animals.sortedBy(propertyName: "type")
// [{name "Tom", type "Cat"}, {name "Sylvester", type "Cat"}, {name "Jerry", type "Mouse"}]
Limitations
The worst limitation of this solutions is that it works only for String properties. It can be change to work with any types of property by it must be at compile time. Right now I have not a solution to make it work with any king of property type without changing the code.
I already asked help for the core of the problem here.
I would definitely recommend simply embedding your dictionary into your struct. A dictionary is a much more suitable data structure for 50 key-value pairs than 50 properties – and you've said that this would be an acceptable solution.
Embedding the dictionary in your struct will give you the best of both worlds – you can easily encapsulate logic & you have have easy lookup of the values for each column ID.
You can now simply sort your array of structures like this:
struct MyStructure {
var dict = [String:String]()
init(col0Data:String, col1Data:String) {
dict["col0data"] = col0Data
dict["col1data"] = col1Data
}
}
var myArray = [MyStructure(col0Data: "foo", col1Data: "bar"), MyStructure(col0Data: "bar", col1Data: "foo")]
var column = "col0data"
myArray.sort {
$0.dict[column] < $1.dict[column]
}
print(myArray) // [MyStructure(dict: ["col0data": "bar", "col1data": "foo"]), MyStructure(dict: ["col0data": "foo", "col1data": "bar"])]
column = "col1data"
myArray.sort {
$0.dict[column] < $1.dict[column]
}
print(myArray) // MyStructure(dict: ["col0data": "foo", "col1data": "bar"])], [MyStructure(dict: ["col0data": "bar", "col1data": "foo"])
Here's an answer (but not the best answer); use subscripts to return the correct property, and set which property you are sorting by within the array.sort:
struct MyStructure {
var col0data = "" //name matches the column identifier
var col1data = ""
subscript(key: String) -> String? { //the key will be the col identifier
get {
if key == "col0data" {
return col0data
} else if key == "col1data" {
return col1data
}
return nil
}
}
}
And then here's how the sort works:
let identifier = the column identifier string,say col0data in this case
myArray.sortInPlace ({
let my0 = $0[identifier]! //the identifier from the table col header
let my1 = $1[identifier]!
return my0 < my1
})
If you do not know what types the values of MyStructure can be you will have a hard time comparing them to sort them. If you had a function that can compare all types you can have in MyStructure then something like this should work
struct OtherTypeNotComparable {
}
struct MyStructure {
var col0data = "cat" //name matches the column identifier
var col1data: OtherTypeNotComparable
}
let structures = [MyStructure(), MyStructure()]
let sortBy = "col1data"
func yourCompare(a: Any, b: Any) -> Bool {
return true
}
var expanded : [[(String, Any, MyStructure)]]
= structures.map { s in Mirror(reflecting: s).children.map { ($0!, $1, s) } }
expanded.sortInPlace { (a, b) -> Bool in
let aMatch = a.filter { $0.0 == sortBy }.first!.1
let bMatch = b.filter { $0.0 == sortBy }.first!.1
return yourCompare(aMatch, b: bMatch)
}
source: https://developer.apple.com/library/watchos/documentation/Swift/Reference/Swift_Mirror_Structure/index.html