sum array of Core Data entity attributes

Question

I have two core data entities, proposal and wageClass, and each has a to-many relationship to the other. WageClass has an Int attribute, numberOfWorkers. I need to sum the array of numberOfWorkers related to each proposal.

Currently I use this:

 let proposalNumberOfWorkers = proposal.value(forKeyPath: "wageClasses.numberOfWorkers")

and when I do this:

 let arraySum = proposalNumberOfWorkers.reduce(0, +)

I get an error that says type Any has no member reduce. When I eliminate the previous line of code and just try to print the array like this:

 totalWorkersLabel.text = "\(proposalNumberOfWorkers!)"

the UILabel looks like this: {(15)}

(15 being either the first or most recent item in the array, I'm not sure which)

So I'm wondering, 1) how do I make it .reduce, and 2) what the brackets and parens are about. Thanks in advance for your comments!

Answer 1

The brackets and parentheses indicate that proposalNumberOfWorkers! is an NSSet. NSSet does not recognise the reduce method. NSSet and Set are bridged, so you can get what you need by casting proposalNumberOfWorkers as a Set:

let proposalNumberOfWorkers = proposal.value(forKeyPath: "wageClasses.numberOfWorkers") as! Set<Int>

and then use reduce.