Swift: For Loop to iterate through enumerated array by index greater than 1

Question

Is there a way to use a for-in loop through an array of strings by an index greater than 1 using .enumerated() and stride, in order to keep the index and the value?

For example, if I had the array

var testArray2: [String] = ["a", "b", "c", "d", "e"]

and I wanted to loop through by using testArray2.enumerated() and also using stride by 2 to output:

0, a
2, c
4, e

So ideally something like this; however, this code will not work:

for (index, str) in stride(from: 0, to: testArray2.count, by: 2){
    print("position \(index) : \(str)")
}

Nirav D · Accepted Answer · 2017-04-25 05:40:17Z

6

You have two ways to get your desired output.

Using only stride

var testArray2: [String] = ["a", "b", "c", "d", "e"]

for index in stride(from: 0, to: testArray2.count, by: 2) {
    print("position \(index) : \(testArray2[index])")
}

Using enumerated() with for in and where.

for (index,item) in testArray2.enumerated() where index % 2 == 0 {
    print("position \(index) : \(item)")
}

answered Apr 25, 2017 at 5:40

Nirav D

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2 Comments

Biggytiny Over a year ago

Thank you, I am just learning Swift and this is all very new syntax for me.

Nirav D Over a year ago

@Biggytiny Welcome mate :) Once you understand the syntax it is looks easy for you too.

Palle · Accepted Answer · 2017-04-25 05:40:42Z

3

To iterate with a stride, you could use a where clause:

for (index, element) in testArray2.enumerated() where index % 2 == 0 {
    // do stuff
}

Another possible way would be to map from indices to a collection of tuples of indices and values:

for (index, element) in stride(from: 0, to: testArray2.count, by: 2).map({($0, testArray2[$0])}) {
    // do stuff
}

answered Apr 25, 2017 at 5:40

Palle

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