ASTDDEV()

  Short:
  ------
  ASTDDEV() Standard deviation of an array with condition

  Returns:
  --------
  <nStdDev> => Standard deviation

  Syntax:
  -------
  ASTDDEV(aTarget,[bCondition])

  Description:
  ------------
  <aTarget> is the target array. Normally an array of
  numeric values. [bCondition] is an optional codeblock used to
  select a subset of the array. This could be used to filter out
  0's or non-numeric elements. The block must accept an array
  element as a parameter, and return true or false <expL> to
  determine if this element is part of the desired subset.

  Examples:
  ---------
   v := ASTDDEV(aSales)
   v := ASTDDEV(aSales,{|e|valtype(e)=="N".and.e<>0})

  Source:
  -------
  S_ASTATS.PRG