使用 Scala 生成随机序列

Question

I need to get a random sequence of 100 values from 10^-10 to 10^10 and storing to an Array using Scala. I tried following but it didn't work

Array(scala.math.pow(10,-10).doubleValue to scala.math.pow(10,10).intValue by scala.math.pow(10,5).toLong)

Can anyone help me to figure out how to do this correctly?

Answer 1

So you need to fill() the array with Random elements.

import scala.util.Random

val rndm = new Random(1911L)
Array.fill(100)(rndm.between(math.pow(10,-10), math.pow(10,10)))
//res0: Array[Double] = Array(6.08868427907728E9
// , 3.29548545155816E9
// , 9.52802903383275E9
// , 7.981295238889314E9
// , 1.9462480080050848E9
// . . .

This works because the 2nd parameter to the fill() method is "by-name", ie re-evaluated for every element.

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UPDATE

Things aren't quite as clean if you don't have the .between() method (Scala 2.13).

Array.fill(100)(rndm.nextDouble())
     .map(_ * math.pow(10,10))

Note that this actually has a floor of 0.0 instead of the desired 0.0000000001 . It's very unlikely you'd have an entry that's too small, especially when taking only 100 samples. Still, there are steps you could take to insure that can't happen.