Replace value from multi-dimensional array

Question

I have an array made from a struct that holds multiple arrays and when trying to replace a value within the subarray I am met with an error:

Fatal error: Index out of range

  struct Main {
  var city: String
  var pop: Int
  var color: String
}

class Home {
    
var mainArray = [[Main]]()

func update() {
    let data = Main(city: "SF", pop: 2, color: "orange")
    mainArray.append(data)
    
    for var subArray in mainArray {
        for var i in subArray {
          var newCity = "SB"
          
           i.city = newCity
           subArray[0].city = i.city
       }

    }
  }
}

The line starting with var mainArray is not valid Swift code. Please update your question with the actual code you're using. — jnpdx
– jnpdx, Commented Oct 6, 2021 at 19:06

vadian · Accepted Answer · 2021-10-06 19:21:39Z

1

Your code will never work because due to value semantics you are going to modify a copy of the array and subarray.

You have to modify always the original array directly, something like this

struct Main {
  var city: String
  var pop: Int
  var color: String
}

var mainArray = [[Main(city: "SF", pop: 1, color: "blue")], [Main(city: "NYC", pop: 2, color: "white")]]

for (index,  subArray) in mainArray.enumerated() {
    for (subIndex, _) in subArray.enumerated() {
        let newCity = "SB"
        mainArray[index][subIndex].city = newCity
    }
    
}

edited Oct 6, 2021 at 19:21

answered Oct 6, 2021 at 19:14

vadian

286k32 gold badges378 silver badges379 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

catpawsonkeyboard Over a year ago

Thanks for the response. I wanted to indeed modify the original array and was stuck figuring out how but this answer was helpful with finding a solution.

Collectives™ on Stack Overflow

Replace value from multi-dimensional array

1 Answer 1

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Related