I'm having the hardest time figuring out something that seems like it should be very simple. I need to accurately round an NSDecimalNumber to a particular number of decimal places (determined at runtime.) So far as I can tell, I have two options, neither of which I like.
Is there another way that I've missed? There has got to be an easy way to do rounding of NSDecimalNumbers, but I can't seem to figure out for the life of me what it is.
You simply call decimalNumberByRoundingAccordingToBehavior:
with the desired NSDecimalNumberBehaviors
protocol. See the NSDecimalNumberBehaviors
reference in the dev docs .
Update: See http://www.cimgf.com/2008/04/23/cocoa-tutorial-dont-be-lazy-with-nsdecimalnumber-like-me/
For those that prefer example code...
To round to 2 decimal places (12345.68):
NSDecimalNumber *originalNumber = [NSDecimalNumber decimalNumberWithString:@"12345.6789"];
NSDecimalNumberHandler *behavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain
scale:2
raiseOnExactness:NO
raiseOnOverflow:NO
raiseOnUnderflow:NO
raiseOnDivideByZero:NO];
NSDecimalNumber *roundedNumber = [originalNumber decimalNumberByRoundingAccordingToBehavior:behavior];
To round to the nearest thousand (12000):
NSDecimalNumber *originalNumber = [NSDecimalNumber decimalNumberWithString:@"12345.6789"];
NSDecimalNumberHandler *behavior = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain
scale:-3
raiseOnExactness:NO
raiseOnOverflow:NO
raiseOnUnderflow:NO
raiseOnDivideByZero:NO];
NSDecimalNumber *roundedNumber = [originalNumber decimalNumberByRoundingAccordingToBehavior:behavior];
I got it working using the below code in Swift 3.
let amount = NSDecimalNumber(string: "123.456789")
let handler = NSDecimalNumberHandler(roundingMode: .plain, scale: 2, raiseOnExactness: false, raiseOnOverflow: false, raiseOnUnderflow: false, raiseOnDivideByZero: false)
let roundedAmount = amount.rounding(accordingToBehavior: handler)
Note the scale parameter, used to define the decimal places you need. Outlined here: https://developer.apple.com/reference/foundation/nsdecimalnumberhandler/1578295-decimalnumberhandlerwithrounding
I'm using this solution:
import Foundation
extension NSDecimalNumber {
public func round(_ decimals:Int) -> NSDecimalNumber {
return self.rounding(accordingToBehavior:
NSDecimalNumberHandler(roundingMode: .plain,
scale: Int16(decimals),
raiseOnExactness: false,
raiseOnOverflow: false,
raiseOnUnderflow: false,
raiseOnDivideByZero: false))
}
}
let amount = NSDecimalNumber(string: "123.456")
amount.round(2) --> 123.46
amount.round(1) --> 123.5
amount.round(0) --> 123
amount.round(-1) --> 120
amount.round(-2) --> 100
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