I am doing this to loop through my dictionary until until I match the key. My dictionary is defined as [Int:String]
var index = 0
for (key, value) in mylist! {
if key == property.propertyValue as! Int {
// use index here
}
index += 1
}
Is there a better way to do this? I see examples of filtering (something like the example below) but I am not sure how to make it work with a dictionary. Could I use something like this to find the index of the item? Or is there another way?
mylist.filter{$0.key == 1}
UPDATE:
This works:
let index = Array(mylist!.keys).index(of: 1)
But this doesn't:
let index = mylist!.index(forKey: 1)
It seems they both should work. I wonder why the 2nd one doesn't.
A dictionary is an unordered collection type and doesn't have an index.
You can get the value directly by the key
let value = mylist[property.propertyValue as! Int]
If I understand you correctly, you could do it like so:
let myList = [
2: "Hello",
4: "Goodbye",
8: "Whats up",
16: "Hey"
]
let index = Array(myList.keys).index(of: property.propertyValue)
And then to find the key you're looking for again...
let key = Array(myList.keys)[index!]
As said in other answers, a dictionary is probably not the data structure you're looking for. But this should answer the question you've asked.
Given your dictionary
let dict = [1:"a", 2:"b", 3: ""]
you can extract the index of a given key (e.g. `1) simply writing
let indexForKey1 = dict.index(forKey: 1)
Fetching all the indexes
You can also build a dictionary where they key is the index and the value is the key of dict
let indexes = dict.keys.map { dict.index(forKey: $0) }
BTW: what do you really need to do?
Related
As I am new to swift programming language .I am using the dictionary of two items now i need to take the index path of particular dictionary value .I am using the following code
var dictionaryitems = ["computer":"something to make work easy","pen":"used for writing something"]
print(dictionaryitems["pen"])
Use firstIndex for this
let index = dictionaryitems.firstIndex(where: {$0.key == "pen"})
you can get index of key or value by
let index = Array(Dictionary.keys).index(of: key/value)
by this you will get an optional value which you can unwrap using if-let or guard statement for further use
var dictionaryitems = ["computer":"something to make work easy","pen":"used for writing something"]
if let index = dictionaryitems.index(forKey: "pen") {
print(dictionaryitems[index].key, ":", dictionaryitems[index].value)
}
This is an example how you can get the index of a dictionary using swift >
if let index = carDataArray?.index(where: {$0["carName"] as! String == "BMW"}) {
print("Car Found")
}
I'm trying to figure out the best way in Swift to add values to an Array that is a Value in a Dictionary. I want to build a dictionary of contacts sorted by the first letter of their first name. For example [A : [Aaron, Adam, etc...], B : [Brian, Brittany, ect...], ...]
I found this function:
updateValue(_:forKey:)
And tried using it in a loop:
for contact in self.contacts.sorted() {
self.contactDictionary.updateValue([contact], forKey: String(describing: contact.characters.first))
}
But when I tried to use that it replaced the existing array with a new one. I know I can manually check to see if the key in the dictionary exists, if it does, retrieve the array and then append a new value, otherwise add the new key/value pair but I'm not sure if Swift provides an easier/better way to do this.
Any insight would be much appreciated!
You can use reduce(into:) method (Swift4) and as follow:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
// make sure there is at least one letter in your string else return
guard let first = element.first else { return }
// create a string with that initial
let initial = String(first)
// initialize an array with one element or add another element to the existing value
result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
If you are using Swift3 or earlier you would need to create a mutable result dictionary inside the closure:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce([String:[String]]()) { result, element in
var result = result
guard let first = element.first else { return result }
let initial = String(first)
result[initial] = (result[initial] ?? []) + [element]
return result
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
Note that the result is not sorted. A dictionary is an unordered collection. If you need to sort your dictionary and return an array of (key, Value) tuples you can use sorted by key as follow:
let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)
"[(key: "A", value: ["Aaron", "Adam"]), (key: "B", value: ["Brian", "Brittany"])]\n"
Swift 4's new dictionary initializers can do it all for you:
let contactInitials = contacts.filter{!$0.isEmpty}.map{ ($0.first!,[$0]) }
let dict = [Character:[String]](contactInitials, uniquingKeysWith:+)
I'm trying to figure out the best way in Swift to add values to an Array that is a Value in a Dictionary. I want to build a dictionary of contacts sorted by the first letter of their first name. For example [A : [Aaron, Adam, etc...], B : [Brian, Brittany, ect...], ...]
I found this function:
updateValue(_:forKey:)
And tried using it in a loop:
for contact in self.contacts.sorted() {
self.contactDictionary.updateValue([contact], forKey: String(describing: contact.characters.first))
}
But when I tried to use that it replaced the existing array with a new one. I know I can manually check to see if the key in the dictionary exists, if it does, retrieve the array and then append a new value, otherwise add the new key/value pair but I'm not sure if Swift provides an easier/better way to do this.
Any insight would be much appreciated!
You can use reduce(into:) method (Swift4) and as follow:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce(into: [String:[String]]()) { result, element in
// make sure there is at least one letter in your string else return
guard let first = element.first else { return }
// create a string with that initial
let initial = String(first)
// initialize an array with one element or add another element to the existing value
result[initial] = (result[initial] ?? []) + [element]
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
If you are using Swift3 or earlier you would need to create a mutable result dictionary inside the closure:
let contacts = ["Aaron", "Adam", "Brian", "Brittany", ""]
let dictionary = contacts.reduce([String:[String]]()) { result, element in
var result = result
guard let first = element.first else { return result }
let initial = String(first)
result[initial] = (result[initial] ?? []) + [element]
return result
}
print(dictionary) // ["B": ["Brian", "Brittany"], "A": ["Aaron", "Adam"]]
Note that the result is not sorted. A dictionary is an unordered collection. If you need to sort your dictionary and return an array of (key, Value) tuples you can use sorted by key as follow:
let sorted = dictionary.sorted {$0.key < $1.key}
print(sorted)
"[(key: "A", value: ["Aaron", "Adam"]), (key: "B", value: ["Brian", "Brittany"])]\n"
Swift 4's new dictionary initializers can do it all for you:
let contactInitials = contacts.filter{!$0.isEmpty}.map{ ($0.first!,[$0]) }
let dict = [Character:[String]](contactInitials, uniquingKeysWith:+)
Ok, I am working in an iMessage app and am trying to parse more than 1 url query item from the selected message here- I have been successful getting/sending just 1 value in a query:
override func willBecomeActive(with conversation: MSConversation) {
// Called when the extension is about to move from the inactive to active state.
// This will happen when the extension is about to present UI.
if(conversation.selectedMessage?.url != nil) //trying to catch error
{
let components = URLComponents(string: (conversation.selectedMessage?.url?.query?.description)!)
//let val = conversation.selectedMessage?.url?.query?.description
if let queryItems = components?.queryItems {
// process the query items here...
let param1 = queryItems.filter({$0.name == "theirScore"}).first
print("***************=> GOT IT ",param1?.value)
}
}
When I just have 1 value, just by printing conversation.selectedMessage?.url?.query?.description I get an optional with that 1 value, which is good. But with multiple I cant find a clean way to get specific values by key.
What is the correct way to parse a URLQueryItem for given keys for iMessage?
When you do conversation.selectedMessage?.url?.query?.description it simply prints out the contents of the query. If you have multiple items then it would appear something like:
item=Item1&part=Part1&story=Story1
You can parse that one manually by splitting the string on "&" and then splitting the contents of the resulting array on "=" to get the individual key value pairs in to a dictionary. Then, you can directly refer to each value by key to get the specific values, something like this:
var dic = [String:String]()
if let txt = url?.query {
let arr = txt.components(separatedBy:"&")
for item in arr {
let arr2 = item.components(separatedBy:"=")
let key = arr2[0]
let val = arr2[1]
dic[key] = val
}
}
print(dic)
The above gives you an easy way to access the values by key. However, that is a bit more verbose. The way you provided in your code, using a filter on the queryItems array, is the more compact solution :) So you already have the easier/compact solution, but if this approach makes better sense to you personally, you can always go this route ...
Also, if the issue is that you have to write the same filtering code multiple times to get a value from the queryItems array, then you can always have a helper method which takes two parameters, the queryItems array and a String parameter (the key) and returns an optional String value (the value matching the key) along the following lines:
func valueFrom(queryItems:[URLQueryItem], key:String) -> String? {
return queryItems.filter({$0.name == key}).first?.value
}
Then your above code would look like:
if let queryItems = components?.queryItems {
// process the query items here...
let param1 = valueFrom(queryItems:queryItems, key:"item")
print("***************=> GOT IT ", param1)
}
You can use iMessageDataKit library. It makes setting and getting data really easy and straightforward like:
let message: MSMessage = MSMessage()
message.md.set(value: 7, forKey: "user_id")
message.md.set(value: "john", forKey: "username")
message.md.set(values: ["joy", "smile"], forKey: "tags")
print(message.md.integer(forKey: "user_id")!)
print(message.md.string(forKey: "username")!)
print(message.md.values(forKey: "tags")!)
(Disclaimer: I'm the author of iMessageDataKit)
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)]