swift dictionaries: map within a map - swift

Question

I'd like to convert a value I get from an API to a specific format.
[String:Any] // format received
[Int:[ContentType:Int]] // required format
ContentType is an Enum
An example of the data might look like this:
["123":["Tables":"25","Chairs":"14"]] // input
[123:[.Tables:25,.Chairs:14]] // output
I think I need to have a map within a map for this to work, but I'm struggling to work out a way forward. I may well be barking up the wrong tree entirely though. I don't really want to manually loop through and add each item one at a time; I'm looking for something more intelligent than that if possible.
enum ContentType: String {
case Tables,Chairs
}
let original_values: [String:Any]
= ["1234":["Tables":"5","Chairs":"2"]]
let values: [Int:[ContentType:Int]]
= Dictionary(uniqueKeysWithValues: original_values.map {
(
Int($0.key)!,
(($0.value as? [String:String]).map { // Error on this line - expects 1 argument but two were used
(
ContentType(rawValue: $1.key)!, // $1 is presumably wrong here?
Int($1.value)
)
}) as? [ContentType:Int]
)
})
Any ideas anybody?

Answer 1

I'd like to convert a value I get from an API to a specific format.
You can make your enum Decodable
enum ContentType: String, Decodable {
case tables, chairs
enum CodingKeys: String, CodingKey {
case Tables = "Tables"
case Chairs = "Chairs"
}
}
Then you can decode received Data and then compactMap it to format (Int, [ContentType: Int]). These tuples you can convert to Dictionary using designed initializer
do {
let decoded = try JSONDecoder().decode([String: [ContentType: Int]].self, from: data)
let mapped = Dictionary(uniqueKeysWithValues: decoded.compactMap { (key,value) -> (Int, [ContentType: Int])? in
if let int = Int(key) {
return (int, value)
} else {
return nil
}
})
} catch {
print(error)
}

Answer 2

On this line:
(($0.value as? [String:String]).map {
You using not Sequence.map, but Optional.map.
Working solution:
/// First let's map plain types to our types
let resultArray = original_values
.compactMap { (key, value) -> (Int, [ContentType: Int])? in
guard let iKey = Int(key), let dValue = value as? [String: String] else { return nil }
let contentValue = dValue.compactMap { (key, value) -> (ContentType, Int)? in
guard let cKey = ContentType(rawValue: key), let iValue = Int(value) else { return nil }
return (cKey, iValue)
}
let contentDict = Dictionary(uniqueKeysWithValues: contentValue)
return (iKey, contentDict)
}
let result = Dictionary(uniqueKeysWithValues: resultArray)
To improve print output add conform to CustomStringConvertible:
extension ContentType: CustomStringConvertible {
var description: String {
switch self {
case .Tables:
return "Tables"
case .Chairs:
return "Chairs"
}
}
}

Answer 3

This is Swift 5 correct syntax
enum ContentType: String {
case tables = "Tables"
case chairs = "Chairs"
}
let originalValues: [String: [String: String]]
= ["1234": ["Tables": "5", "Chairs": "2"]]
let values: [Int: [ContentType: Int]] = Dictionary(uniqueKeysWithValues:
originalValues.map { arg in
let (key, innerDict) = arg
let outMap: [ContentType: Int] = Dictionary(uniqueKeysWithValues:
innerDict.map { innerArg in
let (innerKey, innerValue) = innerArg
return (ContentType.init(rawValue: innerKey)!, Int(innerValue)!)
}
)
return (Int(key)!, outMap)
}
)
print(values)
[1234: [__lldb_expr_5.ContentType.tables: 5, __lldb_expr_5.ContentType.chairs: 2]]