Core Data: Get most frequent value used for an attribute

Question

How can one get the most frequent value used for an attribute in Core Data?

Let's say that our Entity table is:

--------------------------
|   Name   |   Company   |
--------------------------
|   John   |  Boring Co. |
|   Jane   |  Boring Co. |
|  Robert  |  Boring Co. |
|   Mary   | MoneyPal Co |
|   Jenn   | MoneyPal Co |
--------------------------

My objective is to get the most repeated value as "Company" attribute, i.e. Boring Co. in this example, without fetching every entity and looping through each item if possible.

Do a fetch request for "Company", this results in an Array, then you can use a (counted) set to find the highest occurrence. See also here: https://stackoverflow.com/questions/30545518/how-to-count-occurrences-of-an-element-in-a-swift-array — koen, Oct 25 '18 at 15:04
Maybe [this article](https://www.cocoanetics.com/2017/04/group-by-count-and-sum-in-coredata/) can get you started. — Joakim Danielson, Oct 25 '18 at 15:04

score 0 · Accepted Answer · answered Nov 04 '18 at 21:17

I'd like share what I've ended up using, in case anyone lands on this page looking for the answer to a similar question. My original intention was to use a Core Data/SQL fetching technique or a special predicate of some sorts to achieve this but I think there aren't any. So I implemented the following:

class CoreData_User:NSManagedObject{
    static func getMostFrequentCompany(context: NSManagedObjectContext ) -> String?{
        // We get a list of distinc Company entries
        guard let companies:[String] = CoreData_User.getDistinctCompanies(context: context) else { return nil }

        var maxRepeatedCompany:String = ""
        var maxRepeatCount:Int = 0

        // Then we loop through them to find which one is most oftenly used
        for currentCompany in companies{
            let currentCompanyRepeatCount:Int = CoreData_User.count(withCompany: currentCompany, context: context)
            if currentCompanyRepeatCount > maxRepeatCount{
                maxRepeatedCompany = currentCompany
                maxRepeatCount = currentCompanyRepeatCount
            }
        }
        if maxRepeatCount < 1 || maxRepeatedCompany.isEmpty {
            return nil
        } else {
            return maxRepeatedCompany
        }
    }

    static func getDistinctCompanies(context: NSManagedObjectContext ) -> [String]?{
        let request:NSFetchRequest<NSFetchRequestResult> = CoreData_User.fetchRequest()

        let companyAttributeName:String = "Company"

        request.resultType = .dictionaryResultType
        request.propertiesToFetch = [companyAttributeName]
        request.returnsDistinctResults = true
        var results:[String] = [String]()

        context.performAndWait{
            do{
                guard let fetchResults = try context.fetch(request) as? [NSDictionary] else { return }

                for item in fetchResults{
                    if let company = (item as AnyObject).value(forKey: companyAttributeName) as? String{
                        results.append(company)
                    }
                }
            } catch {
                print("Failed to get company names")
            }
        }

        if results.count > 0 {
            return results
        } else {
            return nil
        }
    }
    static func count(withCompany company: String, context: NSManagedObjectContext) -> Int{
        let request = NSFetchRequest<T>(entityName: type.entity().name!)
        request.includesSubentities = false
        request.predicate = NSPredicate(format: "Company ==[c] %@", company)

        var fetchResult:Int?
        context.performAndWait{
            fetchResult = try? context.count(for: request)
        }

        if let count = fetchResult {
            return count
        } else {
            return 0
        }
    }
}

Any suggestion on ways to improve and optimize is welcomed.

Core Data: Get most frequent value used for an attribute

1 Answers1