Swift - Write an Array to a Text File - arrays

Question

I read into myArray (native Swift) from a file containing a few thousand lines of plain text..
myData = String.stringWithContentsOfFile(myPath, encoding: NSUTF8StringEncoding, error: nil)
var myArray = myData.componentsSeparatedByString("\n")
I change some of the text in myArray (no point pasting any of this code).
Now I want to write the updated contents of myArray to a new file.
I've tried this ..
let myArray2 = myArray as NSArray
myArray2.writeToFile(myPath, atomically: false)
but the file content is then in the plist format.
Is there any way to write an array of text strings to a file (or loop through an array and append each array item to a file) in Swift (or bridged Swift)?

Answer 1

As drewag points out in the accepted post, you can build a string from the array and then use the writeToFile method on the string.
However, you can simply use Swift's Array.joinWithSeparator to accomplish the same with less code and likely better performance.
For example:
// swift 2.0
let array = [ "hello", "goodbye" ]
let joined = array.joinWithSeparator("\n")
do {
try joined.writeToFile(saveToPath, atomically: true, encoding: NSUTF8StringEncoding)
} catch {
// handle error
}
// swift 1.x
let array = [ "hello", "goodbye" ]
let joined = "\n".join(array)
joined.writeToFile(...)

Answer 2

With Swift 5 and I guess with Swift 4 you can use code snippet which works fine to me.
let array = ["hello", "world"]
let joinedStrings = array.joined(separator: "\n")
do {
try joinedStrings.write(toFile: outputURL.path, atomically: true, encoding: .utf8)
} catch let error {
// handle error
print("Error on writing strings to file: \(error)")
}

Answer 3

You need to reduce your array back down to a string:
var output = reduce(array, "") { (existing, toAppend) in
if existing.isEmpty {
return toAppend
}
else {
return "\(existing)\n\(toAppend)"
}
}
output.writeToFile(...)
The reduce method takes a collection and merges it all into a single instance. It takes an initial instance and closure to merge all elements of the collection into that original instance.
My example takes an empty string as its initial instance. The closure then checks if the existing output is empty. If it is, it only has to return the text to append, otherwise, it uses String Interpolation to return the existing output and the new element with a newline in between.
Using various syntactic sugar features from Swift, the whole reduction can be reduced to:
var output = reduce(array, "") { $0.isEmpty ? $1 : "\($0)\n\($1)" }

Answer 4

Swift offers numerous ways to loop through an array. You can loop through the strings and print to a text file one by one. Something like so:
for theString in myArray {
theString.writeToFile(myPath, atomically: false, encoding: NSUTF8StringEncoding, error: nil);
}