Here is the code. The code should counts the standard deviation for double array, but also for Int arrays.
fun calculateSD(numArray: DoubleArray): Double {
var sum = 0.0
var standardDeviation = 0.0
for (num in numArray) {
sum += num
}
val mean = sum / numArray.size
for (num in numArray) {
standardDeviation += Math.pow(num - mean, 2.0)
}
val divider = numArray.size - 1
return Math.sqrt(standardDeviation / divider )
}
You may want to be more idiomatic when working with collections, for instance:
import kotlin.math.pow
import kotlin.math.sqrt
fun sd(data: DoubleArray): Double {
val mean = data.average()
return data
.fold(0.0, { accumulator, next -> accumulator + (next - mean).pow(2.0) })
.let { sqrt(it / data.size )
}
}
BTW, I don't think that data.size - 1 is correct
data.sumOf { (next - mean).pow(2) } instead of aggregate is simpler, but requires kotlin 1.4.
\$\endgroup\$
Something to consider (in general) is whether Math.pow(x, 2.0) is going to be optimized by the interpreter/compiler into x * x or not. The former can be slower if, say, it is computed as Math.exp(Math.log(x) * 2.0).