Convert String to Array of Integers in Swift 3?

Question

I'm trying to write an array of numbers in a file. After reading it, the result is a string, I'm wondering how to read an array of numbers or transform the string into array of numbers?

let file = "sample.txt"
var arr1 = [Int]()
arr1 += 1...100
var text = String(describing: arr1)
var text1 : String = String()
if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {
    let path = dir.appendingPathComponent(file)

    // writing
    do {
        try text.write(to: path, atomically: false, encoding: String.Encoding.utf8)
    }
    catch {/* error handling here */}

    //reading
    do {
        text1 = try String(contentsOf: path, encoding: String.Encoding.utf8)
    }
    catch {/* error handling here */}
}

Now the question is how can I transform text1 into an array of numbers?

you mean convert a string to an array of integers? Try splitting to list of strings, then convert every array item to int (Google it) — user5306470
– user5306470, Commented Jun 4, 2017 at 3:40

vadian · Accepted Answer · 2017-06-04 07:16:09Z

1

The question is: if you want to save an array of Int why do write and read a String?

The easiest way to save an array of Int is the property list format.

Although the recommended way in Swift is the PropertyListSerialization class this writes and reads an array of Int by bridging the Swift Array to NSArray.

let file = "sample.plist"
let arrayToWrite = [Int](1...100)
var arrayToRead = [Int]()

if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {

    let url = dir.appendingPathComponent(file)

    // writing

    (arrayToWrite as NSArray).write(to: url, atomically: false)

    //reading

    arrayToRead = NSArray(contentsOf: url) as! [Int]
    print(arrayToRead)
}

The swiftier way using PropertyListSerialization is

// writing

do {
    let data = try PropertyListSerialization.data(fromPropertyList: arrayToWrite, format: .binary, options: 0)
    try data.write(to: url, options: .atomic)
}
catch { print(error) }

//reading

do {
    let data = try Data(contentsOf: url)
    arrayToRead = try PropertyListSerialization.propertyList(from: data, format: nil) as! [Int]

    print(arrayToRead)
}
catch { print(error) }

edited Jun 4, 2017 at 7:16

answered Jun 4, 2017 at 7:00

vadian

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1 Comment

user3441734 Over a year ago

May be JSONSerialization is another possibility how to do it easy and the "right way".

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