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I have a dictionary with this structure:
a: [1,2]
b: [3,4]
c: [5,6]
and I need to return a string with this structure.
a,b,c\n1,3,5\n2,4,6
I solved the first part of the string. But to get the rest of the String. I try to iterate into my dictionary to get the first elements for each key in my dictionary and then get the rest for each value into the array.
Is there an easier way to get this?
Once you know what's the order of the keys (alpha ?), you can use this:
let dict: [String: [Int]] = ["a": [1,2], "b": [3, 4], "c": [5, 6]]
let keys = dict.keys.sorted() //Or do whatever you want here to get your target order
var matrix: [[String]] = []
keys.forEach {
guard let arrayAsInt = dict[$0] else { return }
let arrayAsString = arrayAsInt.map{ "\($0)" }
matrix.append( [$0] + arrayAsString)
}
print("Matrix: \(matrix)")
let transposed = matrix.transposed()
print("Transposed Matrix: \(transposed)")
let output = transposed.map { $0.joined(separator: ",")}.joined(separator: "\n")
print(output)
The outputs:
$>Matrix: [["a", "1", "2"], ["b", "3", "4"], ["c", "5", "6"]]
$>Transposed Matrix: [["a", "b", "c"], ["1", "3", "5"], ["2", "4", "6"]]
$>a,b,c
1,3,5
2,4,6
Obvisouly the "\n" might be invisible and be an actual new line
a,b,c
1,3,5
2,4,6
Being
a,b,c\n1,3,5\n2,4,6
What's the idea behind that? Create a matrix and use the transpose (it's used in maths with matrix, it's one of the basic modification of a matrix).
First transform the [String: [Int]] into a [[String]], where each element would be key followed by its values. I transformed it there as String for simpler code later.
Why doing that? Because the matrix value is easy to get from your initial dict. the transposed value is harder (not impossible) to get from dict but easier from matrix, and the transposed is quickly transformed into your format.
So my thinking was the reverse:
Get a structure from your output, then how to get it, it's a transpose, so I need to get the initial input as it, etc.
With the help of a code for Transpose Matrix (that accept String elements).
extension Collection where Self.Iterator.Element: RandomAccessCollection {
// PRECONDITION: `self` must be rectangular, i.e. every row has equal size.
func transposed() -> [[Self.Iterator.Element.Iterator.Element]] {
guard let firstRow = self.first else { return [] }
return firstRow.indices.map { index in
self.map{ $0[index] }
}
}
}
Any code (there a various) working ones, should the trick. I took it from here.
As pointed by #Leo Dabus, you can remove the Self.Iterator.Element
from the extension code (twice). I just wanted to it as such, not modifying the initial answer since it's not mind.
What you are looking for, besides composing the final string, is how to transpose a collection (this would work with collections of different sizes as well):
extension Sequence {
func max<T: Comparable>(_ predicate: (Element) -> T) -> Element? {
self.max(by: { predicate($0) < predicate($1) })
}
}
extension Collection where Element: RandomAccessCollection, Element.Indices == Range<Int> {
func transposed() -> [[Element.Element]] {
(0..<(max(\.count)?.count ?? .zero)).map {
index in compactMap { $0.indices ~= index ? $0[index] : nil }
}
}
}
let dict = ["a": [1,2,3],
"b": [4,5,6],
"c": [7,8,9]]
let sorted = dict.sorted(by: {$0.key < $1.key})
let result = sorted.map(\.key).joined(separator: ",") + "\n" +
sorted.map(\.value).transposed().map {
$0.map(String.init).joined(separator: ",")
}.joined(separator: "\n")
result // "a,b,c\n1,4,7\n2,5,8\n3,6,9"
A dictionary is an unordered collection so you need to sort it according to any specific key. Here I sort the dictionary according to the key if you don't care about an order you can just remove sort.
let dict: [String: Any] = ["a": [1,2], "b": [3,4], "c": [5,6]]
let sortedKey = dict.keys.sorted(by: <)
let key = sortedKey.joined(separator: ",")
var firstValues: [String] = []
var secondValues: [String] = []
sortedKey.forEach { (key) in
if let dictValue = dict[key] as? [Int],
let firstValue = dictValue.first,
let secondValue = dictValue.last {
firstValues.append("\(firstValue)")
secondValues.append("\(secondValue)")
}
}
let finalString = key + "\n" + firstValues.joined(separator: ",") + "\n" + secondValues.joined(separator: ",")
print(finalString) // "a,b,c\n1,3,5\n2,4,6"
In Swift 4 I could the code below worked but in Swift 5 I get the following error: Type 'Dictionary<String, String>.Values.Iterator' does not conform to protocol 'Sequence'
guard let userIds = users.values.makeIterator() else { return }
for userId in userIds {
// User setup
}
What is the right way in Swift 5 now?
let dictionary: [String: Int] = ["a": 1, "b": 2]
for (key, value) in dictionary {
print(key, value)
}
You can do simply
for (_, userId) in users {
// User setup
}
You may try iterator like this:
let users = ["a":11, "b":12]
var userIds = users.values.makeIterator()
while let next = userIds.next() {
print(next) // 11 \n 12
}
Also:
let x = [
"kitty": 7,
"bob": 2,
"orange": 44
]
x.forEach { t in
print("key = \(t.key); value = \(t.value)")
}
This has apparently been available since Swift 3. Link to standard library docs on Dictionary type.
Swift 4, swift5 and above
let dict: [String: Any] = ["a": 1, "b": "hello", "c": 3]
for (key, value) in dict {
print(key, value)
}
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:+)
I have a simple Dictionary which is defined like:
var dict : NSDictionary = [ 1 : "abc", 2 : "cde"]
Now I want to add an element into this dictionary: 3 : "efg"
How can I append 3 : "efg" into this existing dictionary?
You're using NSDictionary. Unless you explicitly need it to be that type for some reason, I recommend using a Swift dictionary.
You can pass a Swift dictionary to any function expecting NSDictionary without any extra work, because Dictionary<> and NSDictionary seamlessly bridge to each other. The advantage of the native Swift way is that the dictionary uses generic types, so if you define it with Int as the key and String as the value, you cannot mistakenly use keys and values of different types. (The compiler checks the types on your behalf.)
Based on what I see in your code, your dictionary uses Int as the key and String as the value. To create an instance and add an item at a later time you can use this code:
var dict = [1: "abc", 2: "cde"] // dict is of type Dictionary<Int, String>
dict[3] = "efg"
If you later need to assign it to a variable of NSDictionary type, just do an explicit cast:
let nsDict = dict as! NSDictionary
And, as mentioned earlier, if you want to pass it to a function expecting NSDictionary, pass it as-is without any cast or conversion.
you can add using the following way and change Dictionary to NSMutableDictionary
dict["key"] = "value"
I know this might be coming very late, but it may prove useful to someone.
So for appending key value pairs to dictionaries in swift, you can use updateValue(value: , forKey: ) method as follows :
var dict = [ 1 : "abc", 2 : "cde"]
dict.updateValue("efg", forKey: 3)
print(dict)
SWIFT 3 - XCODE 8.1
var dictionary = [Int:String]()
dictionary.updateValue(value: "Hola", forKey: 1)
dictionary.updateValue(value: "Hello", forKey: 2)
dictionary.updateValue(value: "Aloha", forKey: 3)
So, your dictionary contains:
dictionary[1: Hola, 2: Hello, 3: Aloha]
If your dictionary is Int to String you can do simply:
dict[3] = "efg"
If you mean adding elements to the value of the dictionary a possible solution:
var dict = Dictionary<String, Array<Int>>()
dict["key"]! += [1]
dict["key"]!.append(1)
dict["key"]?.append(1)
Swift 3+
Example to assign new values to Dictionary. You need to declare it as NSMutableDictionary:
var myDictionary: NSMutableDictionary = [:]
let newValue = 1
myDictionary["newKey"] = newValue
print(myDictionary)
For whoever reading this for swift 5.1+
// 1. Using updateValue to update the given key or add new if doesn't exist
var dictionary = [Int:String]()
dictionary.updateValue("egf", forKey: 3)
// 2. Using a dictionary[key]
var dictionary = [Int:String]()
dictionary[key] = "value"
// 3. Using subscript and mutating append for the value
var dictionary = [Int:[String]]()
dictionary[key, default: ["val"]].append("value")
In Swift, if you are using NSDictionary, you can use setValue:
dict.setValue("value", forKey: "key")
Given two dictionaries as below:
var dic1 = ["a": 1, "c": 2]
var dic2 = ["e": 3, "f": 4]
Here is how you can add all the items from dic2 to dic1:
dic2.forEach {
dic1[$0.key] = $0.value
}
Dict.updateValue updates value for existing key from dictionary or adds new new key-value pair if key does not exists.
Example-
var caseStatusParams: [String: AnyObject] = ["userId" : UserDefault.userID ]
caseStatusParams.updateValue("Hello" as AnyObject, forKey: "otherNotes")
Result-
▿ : 2 elements
- key : "userId"
- value : 866
▿ : 2 elements
- key : "otherNotes"
- value : "Hello"
[String:Any]
For the fellows using [String:Any] instead of Dictionary below is the extension
extension Dictionary where Key == String, Value == Any {
mutating func append(anotherDict:[String:Any]) {
for (key, value) in anotherDict {
self.updateValue(value, forKey: key)
}
}
}
As of Swift 5, the following code collection works.
// main dict to start with
var myDict : Dictionary = [ 1 : "abc", 2 : "cde"]
// dict(s) to be added to main dict
let myDictToMergeWith : Dictionary = [ 5 : "l m n"]
let myDictUpdated : Dictionary = [ 5 : "lmn"]
let myDictToBeMapped : Dictionary = [ 6 : "opq"]
myDict[3]="fgh"
myDict.updateValue("ijk", forKey: 4)
myDict.merge(myDictToMergeWith){(current, _) in current}
print(myDict)
myDict.merge(myDictUpdated){(_, new) in new}
print(myDict)
myDictToBeMapped.map {
myDict[$0.0] = $0.1
}
print(myDict)
To add new elements just set:
listParameters["your parameter"] = value
There is no function to append the data in dictionary. You just assign the value against new key in existing dictionary. it will automatically add value to the dictionary.
var param = ["Name":"Aloha","user" : "Aloha 2"]
param["questions"] = "Are you mine?"
print(param)
The output will be like
["Name":"Aloha","user" : "Aloha 2","questions" : ""Are you mine"?"]
To append a new key-value pair to a dictionary you simply have to set the value for the key. for eg.
// Initialize the Dictionary
var dict = ["name": "John", "surname": "Doe"]
// Add a new key with a value
dict["email"] = "john.doe#email.com"
print(dict)
Output -> ["surname": "Doe", "name": "John", "email": "john.doe#email.com"]
var dict = ["name": "Samira", "surname": "Sami"]
// Add a new enter code herekey with a value
dict["email"] = "sample#email.com"
print(dict)
Up till now the best way I have found to append data to a dictionary by using one of the higher order functions of Swift i.e. "reduce". Follow below code snippet:
newDictionary = oldDictionary.reduce(*newDictionary*) { r, e in var r = r; r[e.0] = e.1; return r }
#Dharmesh In your case, it will be,
newDictionary = dict.reduce([3 : "efg"]) { r, e in var r = r; r[e.0] = e.1; return r }
Please let me know if you find any issues in using above syntax.
Swift 5 happy coding
var tempDicData = NSMutableDictionary()
for temp in answerList {
tempDicData.setValue("your value", forKey: "your key")
}
I added Dictionary extension
extension Dictionary {
func cloneWith(_ dict: [Key: Value]) -> [Key: Value] {
var result = self
dict.forEach { key, value in result[key] = value }
return result
}
}
you can use cloneWith like this
newDictionary = dict.reduce([3 : "efg"]) { r, e in r.cloneWith(e) }
if you want to modify or update NSDictionary then
first of all typecast it as NSMutableDictionary
let newdictionary = NSDictionary as NSMutableDictionary
then simply use
newdictionary.setValue(value: AnyObject?, forKey: String)