Take a number and sum its digits raised to the consecutive powers
Recommendations:


For starters I would recommend passing an Int to your function and then converting it to a String before splitting it up and mapping it to its digit components. 
Next, Scala has a useful built in function called zipWithIndex that you could use over (myDigits.indices zip myDigits). Granted it will reverse the ordering from what you have, but that can be handled as you can see in the code below. 
I would also recommend splitting any map / filter / etc over multiple lines to increase readability. 
When you are using reduce to sum the elements of a container you can instead apply the built in sum method.
Finally, I would hold off on converting the (1 to 100) from a Range to a List until after your filter operation is complete.


Code: 

def f(i: Int): Int ={
  val myDigits = i.toString.map(_.asDigit)

  myDigits.zipWithIndex.map { case (y, x) =&gt;
    pow(y, x+1).toInt
  }.sum
}

val x = (1 to 100).filter(i =&gt; i == f(i)).toList