How to Iterate through an array in swift - arrays

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

Answer 1

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: +)}
}

Answer 2

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)")
}

Answer 3

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)
}