Iterate through Swift array and change values

Question

I need to change values of a Swift array. My first try was to just iterate through but this does not work as I only get a copy of each element and the changes do not affect the origin array. Goal is to have a unique "index" in each array element.

myArray = [["index": 0], ["index":0], ["index":0], ["index":0]]

counter = 0
for item in myArray {
  item["index"] = counter
  counter += 1
}

My next attempt was using map but I don't know how to set an increasing value. I could set the $0["index"] = 1 but I need an increasing value. In which way would this be possible using map?

myArray.map( { $0["index"] = ...? } )

Thanks for any help!

Answer 1

The counter in a for loop is a constant. To make it mutable, you could use :

for var item in myArray { ... }

But that won't be helpful here since we'd be mutating item and not the elements in myArray.

You could mutate the elements in myArray this way :

var myArray = [["index": 0], ["index":0], ["index":0], ["index":0]]

var counter = 0

for i in myArray.indices {
    myArray[i]["index"] = counter
    counter += 1
}

print(myArray) //[["index": 0], ["index": 1], ["index": 2], ["index": 3]]

---

The counter variable is not needed here :

for i in myArray.indices {
    myArray[i]["index"] = i
}

---

A functional way of writing the above would be :

myArray.indices.forEach { myArray[$0]["index"] = $0 }