String into array in Swift 3 - arrays

Question

I am trying to transform a string of the following format into an array (...of arrays, of floats!) in Swift 3:
"[173.0, 180.5],[173.0, 180.0],[174.0, 180.5],[174.0, 183.0]"
so that the output would be an array in this format:
[[173.0, 180.5, 173.0, 180.0],[174.0, 180.5, 174.0, 183.0]]
I am really new to Swift and struggling to find any String functions that will allow me to convert the data in this way. Any pointers on how I can do it would be awesome - thanks!

Answer 1

As Martin said, you first want to first convert this from a string to an array. In Swift 3:
let string = "[173.0, 180.5],[173.0, 180.0],[174.0, 180.5],[174.0, 183.0]"
let jsonString = "[" + string + "]"
guard let data = jsonString.data(using: .utf8),
let json = try? JSONSerialization.jsonObject(with: data),
let numberPairs = json as? [[Double]] else {
fatalError("string was not well-formed: \(string)")
}
You then want to combine these pairs of numbers together:
var combinedNumbers = [[Double]]()
var current: [Double]?
for numberPair in numberPairs {
if current != nil {
combinedNumbers.append(current! + numberPair)
current = nil
} else {
current = numberPair
}
}
// use `combinedNumbers` here
Clearly, you should use better variable names (perhaps something that suggests what these sets of numbers are), but hopefully this illustrates the idea.

Answer 2

Swift 4
You can use Decodable:
let str = "[173.0, 180.5],[173.0, 180.0],[174.0, 180.5],[174.0, 183.0]"
let json = "[\(str)]".data(using: .utf8)!
let numbers = try JSONDecoder().decode([[Double]].self, from: json).flatMap { $0 }
let result = stride(from: 0, to: numbers.count, by: 4).map { startIndex -> [Double] in
let endIndex = min(startIndex + 4, numbers.count)
return Array(numbers[startIndex..<endIndex])
}
Swift 3
One option is to use the old-school NSScanner to extract the numbers from the string to a flat array, then build a 2 dimensional array off that:
let str = "[173.0, 180.5],[173.0, 180.0],[174.0, 180.5],[174.0, 183.0]"
let scanner = Scanner(string: str)
scanner.charactersToBeSkipped = CharacterSet(charactersIn: "[], ")
// Build the flat array
var numbers = [Double]()
while !scanner.isAtEnd {
var d = 0.0
if scanner.scanDouble(&d) {
numbers.append(d)
}
}
// Now the 2 dimensional array
let result = stride(from: 0, to: numbers.count, by: 4).map { startIndex -> [Double] in
let endIndex = min(startIndex + 4, numbers.count)
return Array(numbers[startIndex..<endIndex])
}

Answer 3

One option to convert the data types would be to develop a simple algorithm that will iterate through the string and analyze elements and square bracket delimiters, returning the appropriate conversion.
Below is the skeleton of what the fundamental components of such a function could look like.
Included are some basic aspects of the conversion from string to array.
var str = "[173.0, 180.5], [173.0, 180.0],[174.0, 180.5],[174.0, 183.0]"
// Cast returns array ["[","1","7","3",".","0",",".......]
let array = Array(str.characters)
// Iterate through array
for char in array {
if char == "[" || char == "]" {
// Deal with array delimiters appropriately
}
...
}
It might help to check out this similar problem.
NOTE: As Martin R mentioned, JSON interpretation may be a good method as well.