How to append elements into a dictionary in Swift?

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)

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)
        }
    }
}

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")

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)

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 add new elements just set:

listParameters["your parameter"] = value

var dict = ["name": "Samira", "surname": "Sami"]
// Add a new enter code herekey with a value
dict["email"] = "sample@email.com"
print(dict)

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": "[email protected]"]

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)