Swift - inserting array inside array

Question

I've run into a problem, and I can not find a solution. I have an array where I store the start x and end x locations of different objects

placedArray : [[String: [Int: [String: String]]]]

placedArray = [["auto": [0: ["x-start": "300", "x-end": "400"]]], ["bus": [0: ["x-start": "0", "x-end": "300"]]]]

I want to add one more auto to the list, so what I try to do is:

placedArray["auto"].append([1: ["x-start": "400", "x-end": "500"]])

Error:

Cannot subscript a value of type '[[String : [Int : [String : String]]]]' with an index of type 'String'

I would like to get at the end

placedArray = [["auto": [0: ["x-start": "300", "x-end": "400"], 1: ["x-start": "300", "x-end": "400"]]], ["bus": [0: ["x-start": "0", "x-end": "300"]]]]

You have an array of dictionaries. Array can only be subscripted with an integer, you subscripted it with a string. Anyhow, time to define a struct or a class instead of shoving everything into a dictionary — Code Different
– Code Different, Commented Nov 21, 2017 at 15:33

vadian · Accepted Answer · 2017-11-21 16:13:41Z

Two issues:

The outer object is an array, so it must be subscripted with Int index (that's the statement of the error message).
The value for key auto is a dictionary, so you cannot append something.

You have to get the first item of placedArray – which is the auto entry – and then set the value for key 1.

var placedArray : [[String: [Int: [String: String]]]]
placedArray = [["auto": [0: ["x-start": "300", "x-end": "400"]]], ["bus": [0: ["x-start": "0", "x-end": "300"]]]]
placedArray[0]["auto"]?[1] = ["x-start": "400", "x-end": "500"]
print(placedArray)

The line to append 😉 the value can also be written as

placedArray[0]["auto"]?.updateValue(["x-start": "400", "x-end": "500"], forKey: 1)

Nevertheless this kind of nested array / dictionary is very confusing. How about a (very simple) struct based solution:

struct XValue { let start, end : String }

struct Vehicle {
    let name : String
    var xValues : [XValue]

    mutating func add(xValue : XValue) {
        xValues.append(xValue)
    }
}

var placedArray = [Vehicle(name: "auto", xValues: [XValue(start:"300", end: "400")]),
                   Vehicle(name: "bus", xValues: [XValue(start:"0", end: "300")])]

placedArray[0].add(xValue: XValue(start:"400", end: "500"))
print(placedArray)

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