Swift: String from float without rounding the values

Question

1. It is recommended to round the decimals but i am facing an scenario where i just need to cut down the precision.

2. Output: 15.96 to 16.0

3. Desired output: 15.96 to 15.9

Codes:

var value: AnyObject = dict.valueForKey("XXX")!
  var stringVal = NSString(format:"%.1f", value.floatValue)

I thought this will be simple but found tricky. Your thoughts on this is highly appreciated.

Answer 1

Use a NSNumberFormatter and configure its rounding mode accordingly:

let formatter = NSNumberFormatter()
formatter.maximumFractionDigits = 1
formatter.roundingMode = .RoundDown
let s = formatter.stringFromNumber(15.96)
// Result: s = "15.9"

Answer 2

Try using this:

    var test : AnyObject = "15.96"
    var rounded_down = floorf(test.floatValue * 10) / 10;
    print(rounded_down)

Answer 3

Here's an updated answer in Swift 5 based on @Clafou 's answer. You can use it as an extension to any data type. Example

extension Double {    
    func cutToDecimalPlace(_ decimalPlaces: Int) -> String{
        let formatter = NumberFormatter()
        formatter.maximumFractionDigits = decimalPlaces
        formatter.roundingMode = .down
        return formatter.string(from: NSNumber(value: self)) ?? ""
    }
}

And you can call it like this

let priceValueString = "24.124"
let updatedPriceValue = priceValueString.doubleValue.cutToDecimalPlace(1)

Output will be 24.1