How to combine two Dictionary instances in Swift?
IosJsonXcodeDictionarySwiftIos Problem Overview
How do I append one Dictionary
to another Dictionary
using Swift
?
I am using the AlamoFire
library to send a JSON
to a REST server
.
Dictionary 1
var dict1: [String: AnyObject] = [
kFacebook: [
kToken: token
]
]
Dictionary 2
var dict2: [String: AnyObject] = [
kRequest: [
kTargetUserId: userId
]
]
How do I combine the two dictionaries to make a new dictionary as shown below?
let parameters: [String: AnyObject] = [
kFacebook: [
kToken: token
],
kRequest: [
kTargetUserId: userId
]
]
I have tried dict1 += dict2
but got a compile error:
>Binary operator '+=' cannot be applied to two '[String : AnyObject]' operands
Ios Solutions
Solution 1 - Ios
I love this approach:
dicFrom.forEach { (key, value) in dicTo[key] = value }
Swift 4 and 5
With Swift 4 Apple introduces a better approach to merge two dictionaries:
let dictionary = ["a": 1, "b": 2]
let newKeyValues = ["a": 3, "b": 4]
let keepingCurrent = dictionary.merging(newKeyValues) { (current, _) in current }
// ["b": 2, "a": 1]
let replacingCurrent = dictionary.merging(newKeyValues) { (_, new) in new }
// ["b": 4, "a": 3]
You have 2 options here (as with most functions operating on containers):
merge
mutates an existing dictionarymerging
returns a new dictionary
Solution 2 - Ios
var d1 = ["a": "b"]
var d2 = ["c": "e"]
extension Dictionary {
mutating func merge(dict: [Key: Value]){
for (k, v) in dict {
updateValue(v, forKey: k)
}
}
}
d1.merge(d2)
Refer to the awesome Dollar & Cent project https://github.com/ankurp/Cent/blob/master/Sources/Dictionary.swift
Solution 3 - Ios
For Swift >= 2.2:
let parameters = dict1.reduce(dict2) { r, e in var r = r; r[e.0] = e.1; return r }
For Swift < 2.2:
let parameters = dict1.reduce(dict2) { (var r, e) in r[e.0] = e.1; return r }
Swift 4 has a new function:
let parameters = dict1.reduce(into: dict2) { (r, e) in r[e.0] = e.1 }
It's really important to dig around the standard library: map
, reduce
, dropFirst
, forEach
etc. are staples of terse code. The functional bits are fun!
Solution 4 - Ios
We can merge dictionaries in a better way using merge keyword
var dictionary = ["a": 1, "b": 2]
/// Keeping existing value for key "a":
dictionary.merge(["a": 3, "c": 4]) { (current, _) in current }
// ["b": 2, "a": 1, "c": 4]
Solution 5 - Ios
extension Dictionary {
static func +=(lhs: inout Self, rhs: Self) {
lhs.merge(rhs) { _ , new in new }
}
static func +=<S: Sequence>(lhs: inout Self, rhs: S) where S.Element == (Key, Value) {
lhs.merge(rhs) { _ , new in new }
}
}
var dic = ["test1": 1]
dic += ["test2": 2]
dic // ["test1": 1, "test2": 2]
dic += [("test2", 3),("test3", 4)]
dic // ["test3": 4, "test1": 1, "test2": 3]
Solution 6 - Ios
SequenceType.forEach
(implemented by Dictionary
) provides an elegant solution to add a dictionary's elements to another dictionary.
dic1.forEach { dic2[$0] = $1 }
For example
func testMergeDictionaries() {
let dic1 = [1:"foo"]
var dic2 = [2:"bar"]
dic1.forEach { dic2[$0] = $1 }
XCTAssertEqual(dic2[1], "foo")
}
Solution 7 - Ios
My needs were different, I wanted to merge and not clobber.
merging:
["b": [1, 2], "s": Set([5, 6]), "a": 1, "d": ["x": 2]]
with
["b": [3, 4], "s": Set([6, 7]), "a": 2, "d": ["y": 4]]
yields:
["b": [1, 2, 3, 4], "s": Set([5, 6, 7]), "a": 2, "d": ["y": 4, "x": 2]]
I was hoping for a simpler solution, but this is what I ended up with. The challenge was in hopping from dynamic typing to static typing, and I used protocols to solve this.
Also worthy of note is that when you use the dictionary literal syntax, you actually get the foundation types, which do not pick up the protocol extensions. I aborted my efforts to support those as I couldn't find an easy to to validate the uniformity of the collection elements.
import UIKit
private protocol Mergable {
func mergeWithSame<T>(right: T) -> T?
}
public extension Dictionary {
/**
Merge Dictionaries
- Parameter left: Dictionary to update
- Parameter right: Source dictionary with values to be merged
- Returns: Merged dictionay
*/
func merge(right:Dictionary) -> Dictionary {
var merged = self
for (k, rv) in right {
// case of existing left value
if let lv = self[k] {
if let lv = lv as? Mergable where lv.dynamicType == rv.dynamicType {
let m = lv.mergeWithSame(rv)
merged[k] = m
}
else if lv is Mergable {
assert(false, "Expected common type for matching keys!")
}
else if !(lv is Mergable), let _ = lv as? NSArray {
assert(false, "Dictionary literals use incompatible Foundation Types")
}
else if !(lv is Mergable), let _ = lv as? NSDictionary {
assert(false, "Dictionary literals use incompatible Foundation Types")
}
else {
merged[k] = rv
}
}
// case of no existing value
else {
merged[k] = rv
}
}
return merged
}
}
extension Array: Mergable {
func mergeWithSame<T>(right: T) -> T? {
if let right = right as? Array {
return (self + right) as? T
}
assert(false)
return nil
}
}
extension Dictionary: Mergable {
func mergeWithSame<T>(right: T) -> T? {
if let right = right as? Dictionary {
return self.merge(right) as? T
}
assert(false)
return nil
}
}
extension Set: Mergable {
func mergeWithSame<T>(right: T) -> T? {
if let right = right as? Set {
return self.union(right) as? T
}
assert(false)
return nil
}
}
var dsa12 = Dictionary<String, Any>()
dsa12["a"] = 1
dsa12["b"] = [1, 2]
dsa12["s"] = Set([5, 6])
dsa12["d"] = ["c":5, "x": 2]
var dsa34 = Dictionary<String, Any>()
dsa34["a"] = 2
dsa34["b"] = [3, 4]
dsa34["s"] = Set([6, 7])
dsa34["d"] = ["c":-5, "y": 4]
//let dsa2 = ["a": 1, "b":a34]
let mdsa3 = dsa12.merge(dsa34)
print("merging:\n\t\(dsa12)\nwith\n\t\(dsa34) \nyields: \n\t\(mdsa3)")
Solution 8 - Ios
Try This Approach
let dict1: [String: AnyObject] = ["kFacebook": ["kToken": "token"]]
let dict2: [String: AnyObject] = ["kRequest": ["kTargetUserId": "userId"]]
var combinedAttributes : NSMutableDictionary!
combinedAttributes = NSMutableDictionary(dictionary: dict1)
combinedAttributes.addEntriesFromDictionary(dict2)
println(combinedAttributes)
It will Print Following :
{
kFacebook = {
kToken = token;
};
kRequest = {
kTargetUserId = userId;
};
}
Hope it helps !!
Solution 9 - Ios
You can use the below code to combine two dictionary instances in Swift:
extension Dictionary {
func merge(dict: Dictionary<Key,Value>) -> Dictionary<Key,Value> {
var mutableCopy = self
for (key, value) in dict {
// If both dictionaries have a value for same key, the value of the other dictionary is used.
mutableCopy[key] = value
}
return mutableCopy
}
}
Solution 10 - Ios
You are using let keyword to declare the dictionary so you can't make the changes to your dictionary as it is used to declare constant.
Change it to var keyword then it will work for you.
var dict1: [String: AnyObject] = [
kFacebook: [
kToken: token
]
]
var dict2: [String: AnyObject] = [
kRequest: [
kTargetUserId: userId
]
]
dict1 += dict2