Swift: Java equivalent of Arrays.copyOfRange for [UInt8]

Question

I am translating a java code to swift, and I want to know what is the equivalent for swift of Arrays.copyOfRange:

public static byte[] copyOfRange(byte[] original, int from, int to)

for my example I want to translate the next line:

Arrays.copyOfRange(packet.value(), 2, packet.length())

Thanks

Don't add the answer to your question. You can post your solution as an answer, or accept one of the existing answers. — Martin R, Nov 12 '18 at 12:51

vacawama · Accepted Answer · 2018-11-12T14:30:52.050

Java's copyOfRange will also pad the resulting array with zeroes if the upper range value is greater than the array length. This function handles that case as well.

This function can be made generic. It works for any type that conforms to ExpressibleByIntegerLiteral which is needed for the 0 padding.

func copyOfRange<T>(arr: [T], from: Int, to: Int) -> [T]? where T: ExpressibleByIntegerLiteral {
    guard from >= 0 && from <= arr.count && from <= to else { return nil }

    var to = to
    var padding = 0

    if to > arr.count {
        padding = to - arr.count
        to = arr.count
    }

    return Array(arr[from..<to]) + [T](repeating: 0, count: padding)
}

Examples:

let arr: [UInt8] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

if let result = copyOfRange(arr: arr, from: 0, to: 3) {
    print(result)  // [0, 1, 2]
}
if let result = copyOfRange(arr: arr, from: 7, to: 12) {
    print(result)  // [7, 8, 9, 0, 0]
}

Shehata Gamal · Answer 2 · 2018-11-12T12:22:34.497

0

You can try

func getRange (arr:[Int],from:Int,to:Int) -> [Int]? {

  if from >= 0 && from < arr.count && to >= 0 && to < arr.count && from < to {

     return Array(arr[from...to])
  }

 return nil
}

May write

extension Array  {

    func getRenage (from:Int,to:Int) -> [Element]? {

        if from >= 0 && from < self.count && to >= 0 && to < self.count && from < to {

            return Array(self[from...to])
        }

        return nil
    }

}

edited Nov 12 '18 at 12:22

answered Nov 12 '18 at 12:05

Shehata Gamal

98,760
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1

Did you check your code before posting? This does not compile. – Martin R Nov 12 '18 at 12:06
I was just about to press "Post Your Answer" when I saw yours come up. Mine was essentially the same. The key part to this answer is the range subscript `arr[from...to]` which is essentially doing the equivalent of `copyOfRange`. (Except that in Swift you can also use this syntax to write to a subset of the array as well as to extract it.) – Steven W. Klassen Nov 12 '18 at 12:08
@MartinR hand write it – Shehata Gamal Nov 12 '18 at 12:09
Thanks for your quick answer, I want to give it a byteArray so I just have to replace Int by UInt8? – Mickael Belhassen Nov 12 '18 at 12:11
@MickaelBelhassen yeah – Shubham Bakshi Nov 12 '18 at 12:12
There is a pretty good discussion of the details of this syntax at https://stackoverflow.com/questions/24034398/new-array-from-index-range-swift – Steven W. Klassen Nov 12 '18 at 12:12
You want `from <= to`. Also, no need to then check `from < arr.count`. – vacawama Nov 12 '18 at 12:24
@vacawama the op can customize it for his needs , he should be aware of all possible cases according to his use case – Shehata Gamal Nov 12 '18 at 12:28
Since you need `0 <= from <= to < arr.count`, you only need to check 3 conditions `from >= 0 && to >= from && to < arr.count`. – vacawama Nov 12 '18 at 12:28
Look at my edit, and change your answer and I could put the subject resolved – Mickael Belhassen Nov 12 '18 at 12:44

score 0 · Answer 3 · answered Nov 12 '18 at 12:15

0

This should definitfly work:

    var array = [1,2,3,4,5,6,7,8,9]
    var partOfArray = array[5...8]
    print(partOfArray)

answered Nov 12 '18 at 12:15

Jonathan

1

1

This answer could be much more helpful if you explain why it is correct ad relate it to the specifics of the question. – Dragonthoughts Nov 12 '18 at 12:30

score 0 · Answer 4 · answered Nov 12 '18 at 12:53

0

Answer

    func getRange(arr: [UInt8], from: Int, to: Int) -> [UInt8]? {

    if from >= 0 && to >= from && to <= arr.count{

        return Array(arr[from..<to])
    }

    return nil
}

answered Nov 12 '18 at 12:53

Mickael Belhassen

2,970
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Swift: Java equivalent of Arrays.copyOfRange for [UInt8]

4 Answers4