Swift String array with arithmetic operators addition operation

Question

I'm fetching value from RealmDB which is in string format. However this string contains values in arithmetic format like below

let values = ["1/2","1/3","2/3","3/5","1/7"]

Now my problem is that I've to return the addition value of whole array. I'm unable to convert it to Double value because the string itself contain arithmetic operator. How to perform addition on above array of string?

I've tried to use NSExpreesion to do the mathematical operation but it's giving nil value.

let expn = NSExpression(format:"1/3")
print(expn.expressionValue(with: nil, context: nil))

Take each string, separate the numbers from the operator, do the actual operation, then sum up all the results. What have you tried? What didn't work? — Eric Aya, Dec 08 '17 at 15:21
@BhumaJ Please refer this link. https://stackoverflow.com/questions/32366645/converting-array-of-string-to-double-and-then-calculating-the-sum-in-swift — swapnil patel, Dec 08 '17 at 15:25
Are you only going to have fractions in the array or are you going to have other operations as well in your strings? — Dávid Pásztor, Dec 08 '17 at 15:28
@swapnilpatel I've already mentioned that I'm unable to convert it to double because it has arithmetic operator inside string. — Jay Savsani, Dec 08 '17 at 15:30

score 1 · Accepted Answer · answered Dec 08 '17 at 15:40

You can use a single flatMap on your array to convert the fractional Strings to Doubles. You just have to separate the String into two parts by using String.componenets(separatedBy:), then try converting the String parts into numbers and if that succeeds, do the division.

The "" default value is used during the conversion to Int to make sure your app doesn't crash even if some of the values in the array are not proper fractions.

let fractionStrings = ["1/2","1/3","2/3","3/5","1/7"]
let fractions = fractionStrings.flatMap({ fractionString -> Double? in
    let numbers = fractionString.components(separatedBy: "/")
    if let nominator = Int(numbers.first ?? ""), let denominator = Int(numbers.last ?? "") {
        return Double(nominator)/Double(denominator)
    } else {
        return nil
    }
})
print(fractions)

Output:

[0.5, 0.3333333333333333, 0.6666666666666666, 0.6, 0.1428571428571428]

Swift String array with arithmetic operators addition operation

1 Answers1