How to truncate fraction using NSNumberFormatter - ios

Question

How can I format decimal values with next rules
0.12345 => 0.12
10.12345 => 10.12
100.12345 => 100.1
1000.12345 => 1,000
Please, notice that idea is to take the same space.
C style printf allows to do this using something 4.2%f plus somehow thousands separator but I don't get how to reflect it in Cocoa.
UPDATE
If you didn't notice example says that 0.12345 transformed to 0.12 not to 0.1234.

Answer 1

Since NSNumberFormatter ignores maximumFractionDigits when significant mode enabled I created custom class
class TRNumberFormatter: NSNumberFormatter {
override func stringFromNumber(number: NSNumber) -> String? {
let digitsCount = "\(number.integerValue)".characters.count
let value = self.Tround(number.doubleValue, precision: min(self.maximumIntegerDigits - digitsCount, self.maximumFractionDigits))
return super.stringFromNumber(value)
}
func Tround(value: Double, precision: Int) -> Double {
let divisor = pow(10.0, Double(precision))
return round(value * divisor) / divisor
}
}
To use it just
var numberFormatter: NSNumberFormatter = TRNumberFormatter()
numberFormatter.usesGroupingSeparator = true
numberFormatter.maximumIntegerDigits = 4
numberFormatter.minimumIntegerDigits = 1
numberFormatter.maximumFractionDigits = 2
Results
print(numberFormatter.stringFromNumber(0.12345)) // Optional("0.12")
print(numberFormatter.stringFromNumber(10.12345)) // Optional("10.12")
print(numberFormatter.stringFromNumber(100.12345)) // Optional("100.1")
print(numberFormatter.stringFromNumber(1000.12345)) // Optional("1,000")

Answer 2

this comes close:
#import <Foundation/Foundation.h>
int main(int argc, char *argv[]) {
#autoreleasepool {
NSNumberFormatter *nf = [[NSNumberFormatter alloc] init];
nf.usesSignificantDigits = YES;
nf.maximumSignificantDigits = 4;
nf.usesGroupingSeparator = YES;
NSLog(#"%#", [nf stringFromNumber:#(10.23455)]);
}
}
BUT it disregards the maximum of 2 fraction digits the OP wants and setting maximumFractionDigits=2 doesn't work
seems to me we can't emulate this 4.2%f exactly... without subclassing the whole thing