Scala Doubles, and Precision

Question

Is there a function that can truncate or round a Double? At one point in my code I would like a number like: 1.23456789 to be rounded to 1.23

Answer 1

You can use scala.math.BigDecimal:

BigDecimal(1.23456789).setScale(2, BigDecimal.RoundingMode.HALF_UP).toDouble 

There are a number of other rounding modes, which unfortunately aren't very well documented at present (although their Java equivalents are).

Answer 2

Here's another solution without BigDecimals

Truncate:

(math floor 1.23456789 * 100) / 100 

Round:

(math rint 1.23456789 * 100) / 100 

Or for any double n and precision p:

def truncateAt(n: Double, p: Int): Double = { val s = math pow (10, p); (math floor n * s) / s } 

Similar can be done for the rounding function, this time using currying:

def roundAt(p: Int)(n: Double): Double = { val s = math pow (10, p); (math round n * s) / s } 

which is more reusable, e.g. when rounding money amounts the following could be used:

def roundAt2(n: Double) = roundAt(2)(n)