How can I insert To an 2D array of Strings a String

Question

I have a tableview in which I want to have multiple sections that I load from my server so I need a 2D array.

What I've tried is this:

var sections = [String]()
var district = [[String]]()
if let objects = objects {
    for object in objects {
        let town = object["town"] as! String
        if !self.sections.contains(town){
            self.sections.append(town)
            self.district[self.i].append(object["district"] as! String)
            self.i += 1

        }else{

            let f = self.sections.indexOf(town)
            self.district[f!].append(object["district"] as! String)

        }
    }
}

When I run it I got this message:

Index out of range

I tried to insert my elements with += but it doesn't even let me run it.

I also tried this:

self.district[0][0] = object["district"] as! String

And I got the same error.

You're iterating through object in objects but you have no objects variable declared... — pbush25
– pbush25, Commented Jul 26, 2016 at 13:36
I suppose the start value of i is 0 so when you do self.district[self.i].append ... you are accessing self.district[0] but the array is still empty at this moment. — Eric Aya
– Eric Aya, Commented Jul 26, 2016 at 13:40

Martin R · Accepted Answer · 2016-07-26 18:40:45Z

As mentioned in the comments, the array element with index self.i does not exist in the array self.district when you try to append at

self.district[self.i].append(object["district"] as! String)

and you have to append a new element to self.district first.

You should also get rid of all the forced casts as! which cause the program to crash if they fail. You code could then look like this:

var sections = [String]()
var districts = [[String]]()
if let objects = objects {
    for object in objects {
        if let town = object["town"] as? String,
            let dist = object["district"] as? String {

            if let idx = sections.indexOf(town) {
                districts[idx].append(dist)
            } else {
                sections.append(town)
                districts.append([dist])
            }
        }
    }
}

Alternatively (as suggested in a now deleted comment), store the information in a single array of a custom struct:

struct SectionInfo {
    let town: String
    var districts: [String]
}


var sections = [SectionInfo]()
if let objects = objects {
    for object in objects {
        if let town = object["town"] as? String,
            let dist = object["district"] as? String {

            if let idx = sections.indexOf({ $0.town == town }) {
                sections[idx].districts.append(dist)
            } else {
                sections.append(SectionInfo(town: town, districts: [dist]))
            }
        }
    }
}

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