How to Iterate through an array in swift

Question

Im learning swift and am having a problem Iterating through an array. Here is what I'm trying to do:

func orderStringByOccurence(stringArray: [String]) -> [String: Int]{
    var stringDictionary: [String: Int] = [:]
    for i in 0...stringArray.count {
        if stringDictionary[stringArray[i]] == nil {
            stringDictionary[stringArray[i]] = 1
            stringDictionary
        } else {
            stringDictionary[stringArray[i]]! += 1
        }
    }
    return stringDictionary
}

I don't get an error until I try to call this function. Then I get this error:

EXC_BAD_INSTRUCTION (code=EXC_1386_INVOP, subcode=0x0)

I have tried debugging and found that i get the same error when i try this:

for i in 0...arrayFromString.count{
    print(arrayFromString[i])
}

So how do I iterate through this array? Thanks for helping out a new

Thanks for all the answers

user3839756
– user3839756

2015-11-05 20:52:25 +00:00
Commented Nov 5, 2015 at 20:52 — user3839756
– user3839756, Commented Nov 5, 2015 at 20:52

Charles A. · Accepted Answer · 2020-05-11 22:40:13Z

You need to change

for i in 0...arrayFromString.count

to

for i in 0..<arrayFromString.count

As it is now, you iterate through the array and then one past the end.

You can also use a different style of for loop, which is perhaps a little better:

func orderStringByOccurence(stringArray: [String]) -> [String: Int] {
    var stringDictionary: [String: Int] = [:]
    for string in stringArray {
        if stringDictionary[string] == nil {
            stringDictionary[string] = 1
        } else {
            stringDictionary[string]! += 1
        }
    }
    return stringDictionary
}

Also, you can simplify your logic a bit:

for string in stringArray {
    stringDictionary[string] = stringDictionary[string] ?? 0 + 1
}

Update - For the sake of completeness, I thought I'd add a reduce example here as well. Note that as of Swift 5.1 return statements in single line functions can be implied (SE-0255).

func orderStringByOccurence(stringArray: [String]) -> [String: Int] {
    stringArray.reduce([:]) { result, string in result.merging([string: 1], uniquingKeysWith: +)}
}

Aaron Brager · Accepted Answer · 2015-11-05 20:46:48Z

25

A few more approaches:

let array = ["1", "2", "3"]

You can use forEach with trailing closure syntax:

array.forEach { item in
    print(item)
}

You can use the $0 shorthand:

array.forEach {
    print($0)
}

And if you need the indexes, you can use enumerate():

array.enumerate().forEach { itemTuple in
    print("\(itemTuple.element) is at index \(itemTuple.index)")
}

answered Nov 5, 2015 at 20:46

Aaron Brager

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Comments

OldManMcDonalds · Accepted Answer · 2015-11-05 20:40:51Z

7

It seems you're out of index. A more swift-like approach would be in my opinion not to use the count but to do range-based.

var stringArray = ["1", "2", "3"]
for string in stringArray
{
    print(string)
}

answered Nov 5, 2015 at 20:40

OldManMcDonalds

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