Reduce Array Of Managed Objects In Swift

Question

I am having trouble determining the syntax for reducing an array of a custom managed object subclass in Swift. I have a managed object subclass with a property called amount which is a NSNumber. How do I use the reduce function to get the sum of amount for each item in the array of managed objects. Here is what I have tried, but I get an error stating "could not find member 'amount'".

let reduceSum=myArray.reduce(0) {$0 + $1.amount}

I have looked at this example, but it didn't help since I'm getting the could not find member error.

David L · Accepted Answer · 2014-12-05 03:51:48Z

9

Right after posting this, I tried one more thing and it worked. The error message was misleading and made me think the syntax was wrong but the real issue was I needed to convert the NSNumber to a CGFloat. Here is what worked:

let reduceSum=myArray.reduce(0) {$0 + CGFloat($1.amount)}

answered Dec 5, 2014 at 3:51

David L

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3 Comments

Jason Leach Over a year ago

Why does the that line not need $0.amount?

David L Over a year ago

If you look at the example I cited in my question, that explains it better than I can. From that link "In the reduce code, the first closure argument ($0) is the running total, which starts at zero, and the second parameter ($1) references a Person object in the people array."

user1007522 Over a year ago

But why do we need to cast it to a CGFloat? It works but why?

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