How to separate thousands from a Float value with decimals in Swift - swift

Question

I have the following Float: 1123455432.67899
My desired result is a String: 1,123,455,432.67899
Best case correct , and . based on location (US/Europe)
struct Number {
static let withSeparator: NumberFormatter = {
let formatter = NumberFormatter()
formatter.groupingSeparator = ","
formatter.numberStyle = .decimal
return formatter
}()
}
let myFloat: Float = 1123455432.67899
let myNumber = NSNumber(value: myFloat)
let formatter = Number.withSeparator
if let result = formatter.string(from: myNumber) {
print(result)
}
This formatter works great as long as my Float has no decimals, als soon as I'm having decimals it starts to "calculate". It calculates up/down based on the 3rd decimal number.
What am I missing? What's the best way to get a String: 1,123,455,432.67899 from a Float with no matter how many decimal numbers? Help is very appreciated.
Edit:
My exact function:
func formatValue(_ value: String ) -> String {
if let double = Double(value) {
let formatter = Number.withSeparator
if let result = formatter.string(from: NSNumber(value: double)) {
return result
} else {
return value
}
} else {
return value
}
}
value is always a number for example 5.5555555555. But in this specific case the result = 5.556.

Answer 1

Use Double instead of Float, the value you are specifying is not well representable in Float:
// [... your current code ...]
let myDouble: Double = 1123455432.67899
let myNumber = NSNumber(value: myDouble)
// [... your current code ...]
1,123,455,432.679
The e+XX notation Float has by default is not just for show, it is there because Float cannot store all digits. See:
let myFloat2: Float = 1123455432.67899
print(myFloat2 == 1123455432) // true
let notRepresentable = Float(exactly:1123455432.67899) // nil

Answer 2

Fundamentally, your issue comes from the floating point imprecision of Float. Using a double precision floating point data type (Double) will alleviate this, to an extent.
Also, you shouldn't hardcode the groupingSeperator, but instead let it be inferred from the current locale (which is the default behaviour).
import Foundation
let numberFormatter: NumberFormatter = {
let nf = NumberFormatter()
nf.numberStyle = .decimal
return nf
}()
let myDouble = 1123455432.67899
let myNumber = NSNumber(value: myDouble)
// It's also directly initializable from a literal
// let myNumber: NSNumber = 1123455432.67899
guard let result = numberFormatter.string(from: myNumber) else { fatalError() }
print(result)

Answer 3

In addition to luk2302's answer, I would suggest to add it as a method to a Double extension, as follows:
extension Double {
func formattedString(_ maximumFractionDigits: Int = 5) -> String? {
let numberFormatter = NumberFormatter()
numberFormatter.numberStyle = .decimal
numberFormatter.maximumFractionDigits = maximumFractionDigits
return numberFormatter.string(for:self)
}
}
if let formattedString = 1123455432.67899.formattedString() {
print(formattedString) // 1,123,455,432.67899
}
It might improve the ease of getting the desired string.
Thanks for #rmaddy and #LeoDabus for providing useful notes.