I am a newbie trying hard to create 0.2 from combining a a number and a variable together. But I think I have it all backwards somehow. can anyone help?
//turns a string of '20%' into '2'.
let tipPercent = tip.prefix(1)
//turns the string into a Int of '2'
let tipPercent1: Int = Int(tipPercent) ?? 0
//So now I want to combine the 0. with the variable tipPercent1. this will create '0.2'
let twentyTipamount = (billamount * 0.tipPercent1) + billamount
It seems like you just want to parse a percent string into a number. You should use a NumberFormatter.
let numberFormatter = NumberFormatter()
numberFormatter.locale = Locale(identifier: "en-US_POSIX")
// or whatever other locale that your tip is written in
numberFormatter.numberStyle = .percent
// if the tip cannot be parsed, use 0 as the default
let tipRate = numberFormatter.number(from: tip)?.doubleValue ?? 0
// or you can do something else:
// guard let tipRate = numberFormatter.number(from: tip)?.doubleValue else { ... }
// calculate the amount after tips
let totalAmount = billamount * (1 + tipRate)
Related
I'm trying to properly reduce scale, formatting a float value and returning it as a String in Swift.
For example:
let value: Float = 4.8962965
// formattedFalue should be 4.90 or 4,90 based on localization
let formattedValue = value.formatNumber()
Here is what I did:
extension Float {
func reduceScale(to places: Int) -> Float {
let multiplier = pow(10, Float(places))
let newDecimal = multiplier * self // move the decimal right
let truncated = Float(Int(newDecimal)) // drop the fraction
let originalDecimal = truncated / multiplier // move the decimal back return originalDecimal
}
func formatNumber() -> String {
let num = abs(self)
let numberFormatter = NumberFormatter()
numberFormatter.usesGroupingSeparator = true
numberFormatter.minimumFractionDigits = 0
numberFormatter.maximumFractionDigits = 2
numberFormatter.roundingMode = .up
numberFormatter.numberStyle = .decimal
numberFormatter.locale = // we take it from app settings
let formatted = num.reduceScale(to: 2)
let returningString = numberFormatter.string(from: NSNumber(value: formatted))!
return "\(returningString)"
}
}
But when I use this code I get 4.89 (or 4,89 depending on the localization) instead of 4.90 (or 4,90) as I expect.
Thanks in advance.
You get 4.89 because reduceScale(to:) turns the number into 4.89 (actually, probably 4.89000something because 4.89 cannot be expressed exactly as a binary floating point). When the number formatter truncates this to two decimal places, it naturally rounds it down.
In fact, you don't need reduceScale(to:) at all because the rounding function of the number formatter will do it for you.
Also the final string interpolation is unnecessary because the result of NumberFormatter.string(from:) is automatically bridged to a String?
Also (see comments below by Dávid Pásztor and Sulthan) you can use string(for:) to obviate the NSNumber conversion.
This is what you need
import Foundation
extension Float {
func formatNumber() -> String {
let num = abs(self)
let numberFormatter = NumberFormatter()
numberFormatter.usesGroupingSeparator = true
numberFormatter.minimumFractionDigits = 0
numberFormatter.maximumFractionDigits = 2
numberFormatter.roundingMode = .up
numberFormatter.numberStyle = .decimal
numberFormatter.locale = whatever
return numberFormatter.string(for: num)!
}
}
let value: Float = 4.8962965
// formattedFalue should be 4.90 or 4,90 based on localization
let formattedValue = value.formatNumber() // "4.9"
Solved by following Sulthan's comments:
remove that reduceScale method which is not necessary and it will probably work as expected. You are truncating the decimal to 4.89 which cannot be rounded any more (it is already rounded). – Sulthan 6 hours ago
That's because you have specified minimumFractionDigits = 0. If you always want to display two decimal digits, you will have to set minimumFractionDigits = 2. – Sulthan 5 hours ago
Foundation has a better API now.
In-place, you can use .number:
value.formatted(.number
.precision(.fractionLength(2))
.locale(locale)
)
But it's only available on specific types. For an extension for more than one floating-point type, you'll need to use the equivalent initializer instead:
extension BinaryFloatingPoint {
var formattedTo2Places: String {
formatted(FloatingPointFormatStyle()
.precision(.fractionLength(2))
.locale(locale)
)
}
}
let locale = Locale(identifier: "it")
(4.8962965 as Float).formattedTo2Places // 4,90
I have an precision issue when dealing with currency input using Decimal type. The issue is with the formatter. This is the minimum reproducible code in playground:
let formatter = NumberFormatter()
formatter.numberStyle = .currency
formatter.isLenient = true
formatter.maximumFractionDigits = 2
formatter.generatesDecimalNumbers = true
let text = "89806.9"
let decimal = formatter.number(from: text)?.decimalValue ?? .zero
let string = "\(decimal)"
print(string)
It prints out 89806.89999999999 instead of 89806.9. However, most other numbers are fine (e.g. 8980.9). So I don't think this is a Double vs Decimal problem.
Edit:
The reason I need to use the formatter is that sometimes I need to deal with currency format input:
let text = "$89,806.9"
let decimal = formatter.number(from: text)?.decimalValue ?? .zero
print("\(decimal)") // prints 89806.89999999999
let text2 = "$89,806.9"
let decimal2 = Decimal(string: text2)
print("\(decimal2)") // prints nil
Using the new FormatStyle seems to generate the correct result
let format = Decimal.FormatStyle
.number
.precision(.fractionLength(0...2))
let text = "89806.9"
let value = try! format.parseStrategy.parse(text)
Below is an example parsing a currency using the currency code from the locale
let currencyFormat = Decimal.FormatStyle.Currency
.currency(code: Locale.current.currencyCode!)
.precision(.fractionLength(0...2))
let amount = try! currencyFormat.parseStrategy.parse(text)
Swedish example:
let text = "89806,9 kr"
print(amount)
89806.9
Another option is to use the new init for Decimal that takes a String and a FormatStyle.Currency (or a Number or Percent)
let amount = try Decimal(text, format: currencyFormat)
and to format this value we can use formatted(_:) on Decimal
print(amount.formatted(currencyFormat))
Output (still Swedish):
89 806,9 kr
I agree that this is a surprising bug, and I would open an Apple Feedback about it, but I would also highly recommend switching to Decimal(string:locale:) rather than a formatter, which will achieve your goal (except perhaps the isLenient part).
let x = Decimal(string: text)!
print("\(x)") // 89806.9
If you want to fix fraction digits, you can apply rounding pretty easily with * 100 / 100 conversions through Int. (I'll explain if it's not obvious how to do this; it works for Decimal, though not Double.)
Following Joakim Danielson Answer see this amazing documentation on the format style
Decimal(10.01).formatted(.number.precision(.fractionLength(1))) // 10.0 Decimal(10.01).formatted(.number.precision(.fractionLength(2))) // 10.01 Decimal(10.01).formatted(.number.precision(.fractionLength(3))) // 10.010
Amazingly detailed documentation
If this is strictly a rendering issue and you're just looking to translate a currency value from raw string to formatted string then just do that.
let formatter = NumberFormatter()
formatter.numberStyle = .currency
let raw = "89806.9"
if let double = Double(raw),
let currency = formatter.string(from: NSNumber(value: double)) {
print(currency) // $89,806.90
}
If there is math involved then before you get to the use of string formatters, I would point you to
Why not use Double or Float to represent currency? and
How to round a double to an int using Banker's Rounding in C as great starting points.
I get my response with double value and remove formatter.generatesDecimalNumbers line to get work.
let formatter = NumberFormatter()
formatter.numberStyle = .currency
formatter.isLenient = true
formatter.maximumFractionDigits = 2
//formatter.generatesDecimalNumbers = true // I removed this line
let text = "$89806.9"
let double = formatter.number(from: text)?.doubleValue ?? .zero // converting as double or float
let string = "\(double)"
print(string) // 89806.9
let anotherText = "$0.1"
let anotherDouble = formatter.number(from: anotherText)?.doubleValue ?? .zero // converting as double or float
let anotherString = "\(anotherDouble)"
print(anotherString) // 0.1
I want to sort my Realm object, using one of it properties. It has WBS like format (1.1.3 ,1.1.11, etc) using String as it type.
I'm using RealmSwift 3.11.2 and I've already tried using sorted(by:) and it works! But the 1.1.10 and 1.1.11 will be sorted ahead of 1.1.2
This is the code that I'm using
tasks = tasks.sorted(byKeyPath: "wbs", ascending: true)
I expect the output will be ordered correctly, like [1.1.2, 1.1.10, 1.1.11].
Any help is appreciated, I'm drawing a blank here, is there any way I can do it in Realm ?
You may want to take a minute and do an Internet search on sorting strings.
The issue is that if you have a list of strings like this 1, 2, 3, 10 and they are sorted, they will sort to 1, 10, 2, 3.
This is because how strings are sorted; for this example they are they are generally sorted by the first letter/object in the string (1's) and then by the second letter (0) and so on, so then the strings that start with 1 get grouped up. Then 2's etc.
So you need to either pad them so the formats are the same like
01.01.02, 01.01.10, 01.01.11 etc
which will sort correctly or store the three sections in separate properties as numbers (int's)
class TriadClass {
var first = 0
var second = 0
var third = 0
init(x: Int, y: Int, z: Int) {
self.first = x
self.second = y
self.third = z
}
func getPaddedString() -> String {
let formatter = NumberFormatter()
formatter.format = "00"
let firstNum = NSNumber(value: self.first)
let secondNum = NSNumber(value: self.second)
let thirdNum = NSNumber(value: self.third)
let firstString = formatter.string(from: firstNum)
let secondString = formatter.string(from: secondNum)
let thirdString = formatter.string(from: thirdNum)
let finalString = "\(firstString!).\(secondString!).\(thirdString!)"
return finalString
}
func getPureString() -> String {
let formatter = NumberFormatter()
formatter.format = "0"
let firstNum = NSNumber(value: self.first)
let secondNum = NSNumber(value: self.second)
let thirdNum = NSNumber(value: self.third)
let firstString = formatter.string(from: firstNum)
let secondString = formatter.string(from: secondNum)
let thirdString = formatter.string(from: thirdNum)
let finalString = "\(firstString!).\(secondString!).\(thirdString!)"
return finalString
}
}
Then sort by first, second and third. To get the number for display in the UI I included to functions to format them. Note both functions could be greatly improved and shortened by I left them verbose so you could step through.
The usage would be
let myNum = TriadClass(x: 1, y: 1, z: 10)
let paddedString = myNum.getPaddedString()
print(paddedString)
let nonPaddedString = myNum.getPureString()
print(nonPaddedString)
and an output of
01.01.10
1.1.10
There are a number of other solutions as well but these two are a place to start.
I want to remove the special character , in a string so I can convert the value to a double. How do I do it?
Example:
let stringValue = "4,000.50";
I have tried to use the NumberFormatter but getting nil error
let NF = NumberFormatter();
let value = NF.number(from: stringValue);
//nil
If the number string will always be formatted from a specific locale then you need to set the formatter's locale to match. Without setting the locale, the string won't be parsed if the user's locale using different grouping and decimal formatting.
let stringValue = "4,000.50"
let nf = NumberFormatter()
nf.numberStyle = .decimal
nf.locale = Locale(identifier: "en_US")
let value = nf.number(from: stringValue)
FYI - this is Swift, you don't need semicolons at the end of lines.
Same as #rmaddy but using string replacingOccurrences :
var stringValue = "4,000,000.50"
stringValue = stringValue.replacingOccurrences(of: ",", with: "")
let nf = NumberFormatter()
let value = nf.number(from: stringValue)
print(value)
If you know you're working with currency, you could clean-up the text value for any decimal and thousand separator by leveraging the pattern of consecutive digits. If there are any decimals, they would be the last group and would have exactly two digits (for most currencies). On the basis of this assumption, you don't need to know which separator is used and you would also be resilient to the presence of other characters such as the currency name or symbol:
let textValue = "Balance : 1 200,33 Euros"
let nonDigits = CharacterSet(charactersIn: "01234456789").inverted
let digitGroups = textValue.components(separatedBy:nonDigits).filter{!$0.isEmpty}
let textNumber = digitGroups.dropLast().joined(separator:"")
+ ( digitGroups.last!.characters.count == 2
&& digitGroups.count > 1 ? "." : "" )
+ digitGroups.last!
textNumber // 1200.33
If you just want a sanitized string with only digits and decimals, then in Xcode 9.0+ you can just do:
let originalString = "4,000.00"
let numberString = originalString.filter({ "1234567890.".contains($0) })
// numberString -> "4000.00"
Then, converting your sanitized string to a Float is as easy as
if let num = Float(numberString) {
// do something with float
} else {
// failed to init float with string
}
Making my own formatter like this:
enum Formatters {
enum Number {
static let moneyFormatter: NumberFormatter = {
let mFormatter = NumberFormatter()
mFormatter.numberStyle = NumberFormatter.Style.currency
mFormatter.currencyGroupingSeparator = " "
mFormatter.roundingMode = NumberFormatter.RoundingMode.halfUp
mFormatter.maximumFractionDigits = 0
return mFormatter
}()
}
}
And want to example: if 11 400 then round to 11 000, if 11 500 then 12 000
And etc. But it RoundMode works only with Digits correctly, how it setup for groups?
NumberFormatter has a roundingIncrement property for this purpose:
enum Formatters {
enum Number {
static let moneyFormatter: NumberFormatter = {
let mFormatter = NumberFormatter()
mFormatter.numberStyle = .currency
mFormatter.roundingMode = .halfUp
mFormatter.roundingIncrement = 1_000
mFormatter.maximumFractionDigits = 0
return mFormatter
}()
}
}
let fmt = Formatters.Number.moneyFormatter
print(fmt.string(from: 10_499.99)!) // 10.000 €
print(fmt.string(from: 10_500.00)!) // 11.000 €
However, for some reason unknown to me, this does not work if the
groupingSeparator or currencyGroupingSeparator property is set. Therefore, if you need a non-default grouping separator, you would
have to replace it "manually" in the formatted string.
Of course an alternative is to round the value to the nearest
multiple of 1,000 before formatting it. Example:
let value = 10_499.99
let roundedToThousands = (value / 1000).rounded() * 1000