Concatenate Swift Array of Int to create a new Int

问题:

How can you make an Array<Int> ([1,2,3,4]) into a regular Int (1234)? I can get it to go the other way (splitting up an Int into individual digits), but I can't figure out how to combine the array so that the numbers make up the digits of a new number.

回答1:

This will work:

let digits = [1,2,3,4]
let intValue = digits.reduce(0, combine: {$0*10 + $1})

For Swift 4+ :

let digits = [1,2,3,4]
let intValue = digits.reduce(0, {$0*10 + $1})

Or this compiles in more versions of Swift:

(Thanks to Romulo BM.)

let digits = [1,2,3,4]
let intValue = digits.reduce(0) { return $0*10 + $1 }

---

NOTE

This answer assumes all the Ints contained in the input array are digits -- 0...9 . Other than that, for example, if you want to convert [1,2,3,4, 56] to an Int 123456, you need other ways.

回答2:

You can go through string conversion too:

Int(a.map(String.init).joined())

回答3:

edit/update: Swift 4 or later

If your collection of integers has only single digits elements I suggest using the awesome solution provided by @OOper.

If you would like to join a regular collection of integers into a single integer you would first need to know how to check the number of digits of each integer:

extension BinaryInteger {
    var numberOfDigits: Int {
        return self != 0 ? Int(log10(abs(Double(self)))) + 1 : 1
    }
}

Then you can accumulate the total based on the number of digits of each element:

extension Collection where Element: BinaryInteger {
    var digitsSum: Int { return reduce(0, { $0 + $1.numberOfDigits }) }
    func joined() -> Int? {
        guard digitsSum <= Int.max.numberOfDigits else { return nil }
        //             (total multiplied by 10 powered to number of digits) + value
        return reduce(0) { $0 * Int(pow(10, Double($1.numberOfDigits))) + Int($1) }
    }
}

---

let numbers = [1,2,3,4,56]
let value = numbers.joined()  // 123456

回答4:

Just another solution

let nums:[UInt] = [1, 20, 3, 4]
if let value = Int(nums.map(String.init).reduce("", combine: +)) {
    print(value)
}

This code also works if the values inside the nums array are bigger than 10.

let nums:[UInt] = [10, 20, 30, 40]
if let value = Int(nums.map(String.init).reduce("", combine: +)) {
    print(value) // 10203040
}

This code required the nums array to contain only non negative integers.

回答5:

let number = [1, 2, 3].reduce(0){ $0 * 10 + $1 }

print("result: \(number)") // result: 123

回答6:

You could also do

let digitsArray = [2, 3, 1, 5]
if let number = Int.init(d.flatMap({"\($0)"}).joined()) {
    // do whatever with <number>
}