reduce function is printing an empty dictionary [:] - json

Question

I have reduced my dictionary keys successfully in this question as pseudo-code without a real json model. The goal which I accomplished in the previous question is to return only the keys that have matching values. So the output is a dictionary that looks something like this ["WoW": ["#jade", "#kalel"]. Exactly what I needed. Of course there could be other matches and I'd like to return those as well.
Now that I have a proper json model, the reduce function is printing out an empty dictionary [:]. Is it the type in .reduce(into: [String:[String]]() that is causing the issue?
All the data is printing so the json and model structure must be correct.
json
[
{
"id": "tokenID-tqkif48",
"name": "#jade",
"game": "WoW",
"age": "18"
},
{
"id": "tokenID-fvkif21",
"name": "#kalel",
"game": "WoW",
"age": "20"
}
]
UserModel
public typealias Users = [UserModel]
public struct UserModel: Codable {
public let name: String
public let game: String
// etc...
enum CodingKeys: String, CodingKey {
case name
case game
// etc...
Playground
guard let url = Bundle.main.url(forResource: "Users", withExtension: "json") else {
fatalError()
}
guard let data = try? Data(contentsOf: url) else {
fatalError()
}
let decoder = JSONDecoder()
do {
let response = try decoder.decode([UserModel].self, from: data)
for userModel in response {
let userDict: [String:String] = [ userModel.name:userModel.game ]
let reduction = Dictionary(grouping: userDict.keys) { userDict[$0] ?? "" }.reduce(into: [String:[String]](), { (result, element) in
if element.value.count > 1 {
result[element.key] = element.value
}
})
// error catch etc
}

Answer 1

Your code is too complicated. You can group the array by game simply with
let response = try decoder.decode([UserModel].self, from: data)
let reduction = Dictionary(grouping: response, by: {$0.game}).mapValues{ usermodel in usermodel.map{ $0.name}}

Answer 2

UPDATE I may be mistaking what you want to get. There's another code below and please check the results and choose one you want.
If you want to use reduce(into:updateAccumulatingResult:), you can write something like this.
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(name: String, game: String)] = response.map {($0.name, $0.game)}
let reduction = userArray.reduce(into: [String:[String]]()) {result, element in
if !element.game.isEmpty {
result[element.name, default: []].append(element.game)
}
}
print(reduction)
} catch {
print(error)
}
If you prefer an initializer of Dictionary, this may work:
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(name: String, games: [String])] = response.map {
($0.name, $0.game.isEmpty ? [] : [$0.game])
}
let reduction = Dictionary(userArray) {old, new in old + new}
print(reduction)
} catch {
print(error)
}
Both output:
["#jade": ["WoW"], "#kalel": ["WoW"]]
Anyway, your way of combining loop, Dictionary(grouping:) and reduce(into:) in addition of userDict.keys is making things too complex than they should be.
ADDITION When you want to get a Dictionary with keys as games:
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(game: String, name: String)] = response.compactMap {
$0.game.isEmpty ? nil : ($0.game, $0.name)
}
let reduction = userArray.reduce(into: [String:[String]]()) {result, element in
result[element.game, default: []].append(element.name)
}
print(reduction)
} catch {
print(error)
}
Or:
do {
let response = try decoder.decode([UserModel].self, from: data)
let userArray: [(game: String, names: [String])] = response.compactMap {
$0.game.isEmpty ? nil : ($0.game, [$0.name])
}
let reduction = Dictionary(userArray) {old, new in old + new}
print(reduction)
} catch {
print(error)
}
Output:
["WoW": ["#jade", "#kalel"]]