I have three dictionaries, and I want to merge these. Please Help!
Dictionary 1:
"Abc": {
"Def": {
"Jkl": "xxx",
}
}
Dictionary 2:
"Abc": {
"Ghi": {
"Mno": "yyy",
}
}
Dictionary 3:
"Abc": {
"Ghi": {
"Pqr": "zzz"
}
}
I want the resulting dictionary to group similar values together and it should look like this:
"Abc": {
"Def: {
"Jkl": "xxx"
},
"Ghi": {
"Mno": "yyy",
"Pqr": "zzz"
}
}
Use this recursive method to join two dictionaries
func deepMerge(a: [String: Any], b: [String: Any]) -> [String: Any] {
var result = a
for (key, value) in b {
//Key matches
if let aValue = result[key] {
//Both values are dictionaries
if let aValDict = aValue as? [String: Any], let bValDict = value as? [String: Any] {
result[key] = deepMerge(a: aValDict, b: bValDict)
} else {
//One/both values aren't dictionaries
print("Expected two dictionaries to merge")
}
} else {
//Different keys
return a.merging(b) { (_, new) in new }
}
}
return result
}
Usage
let dict1 = ["Abc": ["Def": ["Jkl": "xxx"]]]
let dict2 = ["Abc": ["Ghi": ["Mno": "yyy"]]]
let dict3 = ["Abc": ["Ghi": ["Pqr": "zzz"]]]
var result = [String: Any]()
for dict in [dict1, dict2, dict3] {
result = deepMerge(a: result, b: dict)
}
print(result)
//["Abc": ["Ghi": ["Pqr": "zzz", "Mno": "yyy"], "Def": ["Jkl": "xxx"]]]
iOSDev solution is good and self-explaining recursive function. I would add here another way to handle dictionaries in using Swift method merging(_:uniquingKeysWith:)
Creates a dictionary by merging key-value pairs in a sequence into the dictionary, using a combining closure to determine the value for duplicate keys.
It is available in Swift since version 4.2
Your solution may look natively
func mergeStandard(_ one: [String: [String: [String: String]]],
_ two: [String: [String: [String: String]]]) -> [String: [String: [String: String]]] {
return one.merging(two) {
$0.merging($1) {
$0.merging($1) { value1, value2 -> String in
return value1 // which is logically wrong, as we should have both values, see the Further Steps section
}
}
}
}
let a = ["Abc": ["Def": ["Jkl": "xxx"]]]
let b = ["Abc": ["Ghi": ["Mno": "yyy"]]]
let c = ["Abc": ["Ghi": ["Pqr": "zzz"]]]
let d = mergeStandard(a, b)
let e = mergeStandard(d, c)
print(e)
//["Abc": ["Def": ["Jkl": "xxx"], "Ghi": ["Mno": "yyy", "Pqr": "zzz"]]]
N.B.! when you try some different input, like
let a = ["Abc": ["Def": ["Jkl": "xxx"]]]
let b = ["Abc": ["Ghi": ["Mno": "yyy", "Pqr": "qqq"]]]
let c = ["Abc": ["Ghi": ["Pqr": "zzz"]]]
Because you have two "Pqr" keys. The code above will select the value "qqq" for the key "Pqr". The another answer - from iOSDev has the same issue. Please, see the solution for this case below.
I would recommend you to change your data structure to [String: [String: [String: [String]]]], so you will have the last value as Sequence of String.
And then you could use the following:
func mergeUpgraded(_ one: [String: [String: [String: [String]]]],
_ two: [String: [String: [String: [String]]]]) -> [String: [String: [String: [String]]]] {
return one.merging(two) {
$0.merging($1) {
$0.merging($1) { (arr1, arr2) -> [String] in
var a = arr1
var b = arr2
a.append(contentsOf: b)
return a
}
}
}
}
let a = ["Abc": ["Def": ["Jkl": ["xxx"]]]]
let b = ["Abc": ["Ghi": ["Mno": "yyy", "Pqr": "qqq"]]]
let c = ["Abc": ["Ghi": ["Pqr": "zzz"]]]
let d = mergeUpgraded(a, b)
let e = mergeUpgraded(d, c)
print(e)
// ["Abc": ["Ghi": ["Mno": ["yyy"], "Pqr": ["qqq", "zzz"]], "Def": ["Jkl": ["xxx"]]]]
Thank you everyone for help! This piece of code worked for me:
private func deepMerge(_ d1: [String: Any], _ d2: [String: Any]) -> [String: Any] {
var result = d1
for (k2, v2) in d2 {
if let v1 = result[k2] as? [String: Any], let v2 = v2 as? [String: Any] {
result[k2] = deepMerge(v1, v2)
} else {
result[k2] = v2
}
}
return result
}