Extracting currency from string - swift2

Question

This is Swift 2.1.
How would you go about extracting an amount from a string that looks like "add egg (£2.00)"? In this example, I would need the "2.00" portion.
Would it be a hard-check looking for whatever's enclosed between the brackets? Or is there a more effective way to do so? I.e. regex or something?

Answer 1

'pure' Swift solution, no brackets necessary
let str = ["add egg £ 2.00",
"the price is $12.00 per unit",
"send €10.22 to somebody",
"invalid $(12)"]
func value(str: String, currency: String)->Double {
var chars = str.characters
let currs = currency.characters
while !currs.contains(chars.popFirst() ?? " ") {}
let arr = chars.split(" ")
guard let value = arr.first,
let d = Double(String(value)) else { return Double.NaN }
return d
}
let values = str.flatMap { value($0, currency: "£$€") }
print(values)
/*
[2.0, 12.0, 10.220000000000001, nan]
*/
if you really need the brackets there, no problem ...
let str = ["add egg (£2.00)",
"the price is ($12.00) per unit",
"send (€10.22) to somebody",
"invalid ($-12)"]
func value(str: String, currency: String)->Double {
var chars = str.characters
let currs = currency.characters
while !currs.contains(chars.popFirst() ?? " ") {}
let arr = chars.split(")")
guard let value = arr.first,
let d = Double(String(value)) else { return Double.NaN }
return d
}
let values = str.flatMap { value($0, currency: "£$€") }
print(values)
/*
[2.0, 12.0, 10.220000000000001, -12.0]
*/

Answer 2

There's many ways to achieve what you want - here's a simple example with a regex.
I'm using (?<=\\()[^\\)]+ to find anything between ( and ), then I use a couple of ranges to extract the values: one for the currency symbol, another for the value.
extension String {
func extractValueBetweenParenthesis() -> (currency: String?, value: String?) {
if let range = self.rangeOfString("(?<=\\()[^\\)]+", options: .RegularExpressionSearch) {
let cr = range.startIndex..<range.startIndex.advancedBy(1)
let vr = range.startIndex.advancedBy(1)..<range.endIndex
return (currency: self.substringWithRange(cr), value: self.substringWithRange(vr))
}
return (nil, nil)
}
}
Call the method on a String then safely unwrap the optional results:
let str = "add egg (£2.00)"
let result = str.extractValueBetweenParenthesis()
if let currency = result.currency, value = result.value {
print("Currency is '\(currency)' and value is '\(value)'")
}
Prints:
Currency is '£' and value is '2.00'

Answer 3

var myString = "add egg (£2.00)"
myString = myString.stringByReplacingOccurrencesOfString("", withString: "")
let components = myString.componentsSeparatedByString("add egg (£")
let finalString = components[1].stringByReplacingOccurrencesOfString(")", withString: "")
print(finalString)
//This prints 2.00