How do I decode a JSON file containing arrays Swift 4? - json

Question

I have a JSON file which I'm trying to decode but am getting an error message:
typeMismatch(Swift.Dictionary, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "Expected to decode Dictionary but found an array instead.", underlyingError: nil))
My code is as follows:
struct Phrase: Decodable {
let sentences: [String]
}
func getFromJSON() {
do {
let jsonURL = Bundle.main.url(forResource: "script", withExtension: "json")
let jsonDecoder = JSONDecoder()
let jsonData = try Data(contentsOf: jsonURL!)
let jsonSentence = try jsonDecoder.decode([Phrase].self, from: jsonData)
debugPrint(jsonSentence)
} catch {
print(error)
}
}
I've been looking at lots of other stack overflow questions and I've noticed that the format of these JSON files are different to mine. They are formatted as dictionaries while mine is like this-
[
["bin blue", "with A 2 soon"],
["set blue", "in A 9 soon"],
["lay blue", "at A 3 please"],
["3 5 zero zero 5 8"],
["place blue", "by A 6 now"],
["lay green", "at B ZERO now"],
["8 9 1 5 4 zero"]
]
I know that the decoder is looking for a dictionary but how do I have it decode the arrays instead?

Answer 1

I think you need
let jsonSentence = try jsonDecoder.decode([[String]].self, from: jsonData)

Answer 2

Your JSON data does not match the structure you want to parse. The JSON is an array of string arrays, whereas you try to parse an array of Phrase objects.
Solution 1: to keep the JSON structure as-is, you need to parse an array of arrays, or to keep the custom model type, by using a type alias:
typealias Phrase = [String]
Solution 2: to keep the struct you defined as-is, you'll have to change the JSON format to this;
[
{ "sentences": ["bin blue", "with A 2 soon"] },
{ "sentences": ["set blue", "in A 9 soon"] },
...
]
Both solutions will work with your getFromJSON implementation.