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Xcode – shape data from core data into plottable format

I have a conceptual question regarding plotting charts in SwiftUI based on data from core data.
Lets say I am building a todo list app and I have a todo entity in core data. This entity has the attributes name and finishDate (the date on which the todo was marked as finished).

To plot these two variables, I need a variable containing each individual day and a variable containing the number of finished tasks on each specific day.

Does anyone know how I would go about creating this data efficiently? I know I can fetch the todo entity data and select the correct attributes. But how do I get the number of finished tasks on each specific day? Ideally without creating those variables using for loops.

It would be really appreciated if anyone can help me.

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2

Answers


  1. 0

    I’d start with an attribute for the day of the week (which you can derive from the Date() value you’re using for completion date). Then you can use either a count fetch request (Cocoa Core Data efficient way to count entities), or a group-by and an NSDictionaryResultType (extensive code example at https://www.cocoanetics.com/2017/04/group-by-count-and-sum-in-coredata/). The group-by approach will give you a dictionary that looks like this (from the Cocoanetics article):

    [
   {
      "count": 111,
      "col": "One"
   },
   {
      "count": 222,
      "col": "Two"
   }
]

    I believe, but don’t know for certain, that you’ll have to compute/store the day-of-week value as an attribute for these grouping approaches to work.

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  2. 0

    This is easy using CoreData + SwiftUI.

    The code below is for iOS15+ but you can do the same thing with an NSFetchedResultsController or NSFetchRequest / @FetchRequest and then group it. But it will require a bit of effort to stay real time.

    Also, the code below is meant to work with the standard Apple code for a CoreData project. The only thing I changed in PersistenceController is setting a random day for the timestamp

    newItem.timestamp = Date().addingTimeInterval(60*60*24*Double(Int.random(in: -10...10)))

    This is a simple graph

    import SwiftUI

@available(iOS 15.0, *)
struct DayChart: View {
    @SectionedFetchRequest(entity: Item.entity(), sectionIdentifier: .completionDate, sortDescriptors: [NSSortDescriptor(keyPath: Item.timestamp, ascending: true)], predicate: nil, animation: Animation.linear)
    var sections: SectionedFetchResults<String, Item>
    @State var maxCount: Int = 1
    let spacing: CGFloat = 3
    var body: some View {
        VStack{
            GeometryReader{ geo in
                HStack(alignment: .bottom, spacing: spacing){
                    ForEach(sections){section in
                        VStack{
                            Text(section.count.description)
                            Rectangle()
                                .foregroundColor(.blue)
                                .onAppear(){
                                    maxCount = max(maxCount,section.count)
                                    
                                }
                            Text(section.id.description).minimumScaleFactor(0.5)
                            .lineLimit(2)
                        }.frame(width: (geo.size.width/CGFloat(sections.count) - spacing),height: geo.size.height * CGFloat(CGFloat(section.count)/CGFloat(maxCount)))
                    }
                }
            }
        }.padding(.leading, spacing)
    }
}

@available(iOS 15.0, *)
struct DayChart_Previews: PreviewProvider {
    static var previews: some View {
        DayChart().environment(.managedObjectContext, PersistenceController.preview.container.viewContext)
    }
}
extension Item{
    //This is the variable that determines your section/column/completion date
    @objc
    var completionDate: String{
                    
        if self.timestamp != nil{
            let dateFormatter: DateFormatter = DateFormatter()
            dateFormatter.dateFormat = "ddnMMM"
            return dateFormatter.string(from: self.timestamp!)
             
        }else{
            return ""
        }
    }
}

    enter image description here

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