Iterate over two arrays simultaneously

Question

I am new to Swift. I have been doing Java programming. I have a scenario to code for in Swift.

The following code is in Java. I need to code in Swift for the following scenario

// With String array - strArr1
String strArr1[] = {"Some1","Some2"}

String strArr2[] = {"Somethingelse1","Somethingelse2"}

for( int i=0;i< strArr1.length;i++){
    System.out.println(strArr1[i] + " - "+ strArr2[i]);
}

I have a couple of arrays in swift

var strArr1: [String] = ["Some1","Some2"]
var strArr2: [String] = ["Somethingelse1","Somethingelse2"]

for data in strArr1{
    println(data)
}

for data in strArr2{
    println(data)
}
// I need to loop over in single for loop based on index.

Could you please provide your help on the syntaxes for looping over based on index

Answer 1

You can use zip(), which creates a sequence of pairs from the two given sequences:

let strArr1 = ["Some1", "Some2"]
let strArr2 = ["Somethingelse1", "Somethingelse2"]

for (e1, e2) in zip(strArr1, strArr2) {
    print("\(e1) - \(e2)")
}

The sequence enumerates only the "common elements" of the given sequences/arrays. If they have different length then the additional elements of the longer array/sequence are simply ignored.

Thus, perfectly safe if the arrays are of different lengths.

Answer 2

With Swift 5, you can use one of the 4 following Playground codes in order to solve your problem.

---

#1. Using zip(_:_:) function

In the simplest case, you can use zip(_:_:) to create a new sequence of pairs (tuple) of the elements of your initial arrays.

let strArr1 = ["Some1", "Some2", "Some3"]
let strArr2 = ["Somethingelse1", "Somethingelse2"]

let sequence = zip(strArr1, strArr2)

for (el1, el2) in sequence {
    print("\(el1) - \(el2)")
}

/*
 prints:
 Some1 - Somethingelse1
 Some2 - Somethingelse2
 */

---

#2. Using Array's makeIterator() method and a while loop

It is also easy to loop over two arrays simultaneously with a simple while loop and iterators:

let strArr1 = ["Some1", "Some2", "Some3"]
let strArr2 = ["Somethingelse1", "Somethingelse2"]

var iter1 = strArr1.makeIterator()
var iter2 = strArr2.makeIterator()

while let el1 = iter1.next(), let el2 = iter2.next() {
    print("\(el1) - \(el2)")
}

/*
 prints:
 Some1 - Somethingelse1
 Some2 - Somethingelse2
 */

---

#3. Using a custom type that conforms to IteratorProtocol

In some circumstances, you may want to create you own type that pairs the elements of your initials arrays. This is possible by making your type conform to IteratorProtocol. Note that by making your type also conform to Sequence protocol, you can use instances of it directly in a for loop:

struct TupleIterator: Sequence, IteratorProtocol {

    private var firstIterator: IndexingIterator<[String]>
    private var secondIterator: IndexingIterator<[String]>

    init(firstArray: [String], secondArray: [String]) {
        self.firstIterator = firstArray.makeIterator()
        self.secondIterator = secondArray.makeIterator()
    }

    mutating func next() -> (String, String)? {
        guard let el1 = firstIterator.next(), let el2 = secondIterator.next() else { return nil }
        return (el1, el2)
    }

}

let strArr1 = ["Some1", "Some2", "Some3"]
let strArr2 = ["Somethingelse1", "Somethingelse2"]

let tupleSequence = TupleIterator(firstArray: strArr1, secondArray: strArr2)

for (el1, el2) in tupleSequence {
    print("\(el1) - \(el2)")
}

/*
 prints:
 Some1 - Somethingelse1
 Some2 - Somethingelse2
 */

---

#4. Using AnyIterator

As an alternative to the previous example, you can use AnyIterator. The following code shows a possible implementation of it inside an Array extension method:

extension Array {

    func pairWithElements(of array: Array) -> AnyIterator<(Element, Element)> {
        var iter1 = self.makeIterator()
        var iter2 = array.makeIterator()

        return AnyIterator({
            guard let el1 = iter1.next(), let el2 = iter2.next() else { return nil }
            return (el1, el2)
        })
    }

}

let strArr1 = ["Some1", "Some2", "Some3"]
let strArr2 = ["Somethingelse1", "Somethingelse2"]

let iterator = strArr1.pairWithElements(of: strArr2)

for (el1, el2) in iterator {
    print("\(el1) - \(el2)")
}

/*
 prints:
 Some1 - Somethingelse1
 Some2 - Somethingelse2
 */

Answer 3

> Incase of unequal count 

let array1 = ["some1","some2"]
let array2 = ["some1","some2","some3"]

var iterated = array1.makeIterator()
let finalArray = array2.map({ 
                 let itemValue = iterated.next()
                 return "\($0)\(itemValue != nil ? "-"+itemValue! : EmptyString)" })

// result : ["some1-some1","some2-some2","some3"]

Answer 4

for(var i = 0; i < strArr1.count ; i++)
{
    println(strArr1[i] + strArr2[i])
}

That should do it. Never used swift before so make sure to test.

Updated to recent Swift syntax

for i in 0..< strArr1.count {
    print(strArr1[i] + strArr2[i])
}

Answer 5

Try This:

zip([0,2,4,6], [1,3,5,7]).forEach {
    print($0,$1)
}

zip([0,2,4,6], [1,3,5,7]).forEach {
    print($0.0,$0.1)
}

Answer 6

You could also enumerate over one array and used the index to look inside the second array:

Swift 1.2:

for (index, element) in enumerate(strArr1) {
    println(element)
    println(strArr2[index])
}

Swift 2:

for (index, element) in strArr1.enumerate() {
    print(element)
    print(strArr2[index])
}

Swift 3:

for (index, element) in strArr1.enumerated() {
    print(element)
    print(strArr2[index])
}

Answer 7

You could use Range if you still want to use for in.

var strArr1: [String] = ["Some1","Some2"]
var strArr2: [String] = ["Somethingelse1","Somethingelse2"]

for i in Range(start: 0, end: strArr1.count) {
    println(strArr1[i] + " - " + strArr2[i])
}