How to round an NSDecimalNumber in swift?

Question

I can't find any resources on this, and I've been trying all sorts of stuff, but nothing works.

According to Apple's documentation, you round an NSDecimalNumber like this:

NSDecimalNumber.decimalNumberByRoundingAccordingToBehavior(<#behavior: NSDecimalNumberBehaviors?#>)

It takes in an NSDecimalNumberBehavior, which I'm unsure how to manipulate since it (1) cannot be initiated into a variable and have it's properties changed, and (2) the roundingMode() method according to the documentation doesn't take any parameters, but Xcode fills in a parameter space for "self".

I'm totally lost on this. Back to the basic question; How can I round an NSDecimalNumber in swift?

Thanks in advance

NSDecimalNumber.decimalNumberByRoundingAccordingToBehavior: is not a class method. This means that you can call on a decimal number instance, to obtain its rounded value. — Ramy Al Zuhouri, Jun 26 '15 at 10:37

score 11 · Accepted Answer · answered Jun 26 '15 at 10:31

11

you can do it like that

let x = 5
let y = 2
let total = x.decimalNumberByDividingBy(y).decimalNumberByRoundingAccordingToBehavior( NSDecimalNumberHandler(roundingMode: NSRoundingMode.RoundUp, scale: 0, raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: false))

answered Jun 26 '15 at 10:31

Özgür Ersil

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Like string manipulation and other things in Swift, is anyone else perturbed by how much code is required to simply do this? – NullHypothesis Jun 09 '17 at 04:14
This is obviously not the correct answer. Why is this the accepted answer? The question was asking about NSDecimalNumber, not about dividing Ints. – Peter Schorn Jul 26 '20 at 11:39

Arkku · Answer 2 · 2015-06-26T10:55:35.727

9

NSDecimalNumberBehaviors is a protocol and thus cannot be instantiated. You need an object of a class conforming to the protocol. Apple provides the class NSDecimalNumberHandler for this purpose, e.g.:

let handler = NSDecimalNumberHandler(roundingMode: NSRoundingMode.RoundBankers, scale: 0, raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: false)
let rounded = dec.decimalNumberByRoundingAccordingToBehavior(handler)

The scale argument is the number of decimals you want, i.e., 0 rounds to an integer.

edited Jun 26 '15 at 10:55

answered Jun 26 '15 at 10:31

Arkku

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Using the defaultDecimalNumberHandler doesn't seem to make any rounding. Can you provide an example? – Naldhelaan Jun 26 '15 at 10:47
@Naldhelaan My bad regarding the default handler, see example for how to construct your own. – Arkku Jun 26 '15 at 10:56

score 2 · Answer 3 · answered Oct 12 '15 at 03:28

// get a decimal num from a string

let num = NSDecimalNumber.init(string: numStr)

// create an NSDecimalNumberHandler instance 

let behaviour = NSDecimalNumberHandler(roundingMode:.RoundUp, 
scale: 1, raiseOnExactness: false, 
raiseOnOverflow: false, raiseOnUnderflow: 
false, raiseOnDivideByZero: false)

// pass the handler to the method decimalNumberByRoundingAccordingToBehaviour.

// This is an instance method on NSDecimalNumber that takes an object that
// conforms to the protocol NSDecimalNumberBehaviors, which NSDecimalNumberHandler does!

let numRounded = num.decimalNumberByRoundingAccordingToBehavior(behaviour)

How to round an NSDecimalNumber in swift?

3 Answers3

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