Nested array error [duplicate] - swift

Question

This question already has answers here:
Arrays and Swift
(3 answers)
Closed 5 years ago.
I know this is a really newbie question but it has thrown me for days and I can't seem to find a solution that I actually understand.
I am trying to make a nested array to store latitude and longitude, however it Xcode/playground throws a EXC_BAD_INSTRUCTION error.
I want to declare, initialise and print the contents of an array. What am I doing wrong?
var arrayLocations:[[Float]] = []
arrayLocations[0] = [27.1750199, 78.0399665]
print("\(arrayLocations[0][0]) and \(arrayLocations[0][1])")

Answer 1

You cannot assign a value to index 0 because there is no index 0 if the array is empty.
You have to append or insert the item:
arrayLocations.append([27.1750199, 78.0399665])

Answer 2

You cannot assign value into 0 position because index 0 is empty.
You can do this in following ways -
With initial value -
var arrayLocations:[[Float]] = [[0.00,0.00]]
arrayLocations[0] = [27.1750199, 78.0399665]
print("\(arrayLocations[0][0]) and \(arrayLocations[0][1])")
Otherwise you can do this using append or insert as vadian's answer.

Answer 3

As vadian said on his answer
You cannot assign a value to index 0 because there is no index 0 if
the array is empty.
You have to append or insert the item:
arrayLocations.append([27.1750199, 78.0399665])
I suggest that you make use of this Collection extension so that your code won't crash often
extension Collection where Indices.Iterator.Element == Index {
/// Returns the element at the specified index if it is within bounds, otherwise nil.
subscript (safe index: Index) -> Generator.Element? {
return indices.contains(index) ? self[index] : nil
}
}
By using this you could just use if let blocks
Sample:
if let aLocation = arrayLocations[safe: 0] {
aLocation = [27.1750199, 78.0399665]
}
This ensures that even if you try to access an object of index 0 your code won't crash.
Suggestion:
Note: This suggestion is not part of the answer, but rather something to improve your code.
It looks like you're trying to create an array of latitude and longitude. Using an array for the latitude and longitude object isn't very wise. I suggest that you create an object instead, it can be a struct or a typeAlias
For example:
struct CoordinateStruct {
var longitude: Float
var latitude: Float
}
/* or */
typealias CoordinateTypeAlias = (latitude: Float, longitude: Float)
/************************* */
// Your code would then look like this
var arrayLocations:[CoordinateStruct] = []
arrayLocations.append(CoordinateStruct(longitude: 27.12312312, latitude: 78.123123))
/* or */
var arrayLocations:[CoordinateTypeAlias] = []
arrayLocations.append((27.12312312, 78.123123))
// Which would make accessing them very easy and readable, like this.
if let aLocation = arrayLocations[safe: 0] {
print(aLocation.longitude)
print(aLocation.latitude)
// instead of this
print(aLocation[0]) // a person who reads your code won't understand this
print(aLocation[1]) // a person who reads your code won't understand this
}