f.scala

def f(s: String) = {
  val xs = s.split("\n").map(_.split(","))
  val ys = xs.transpose.map(_.map(_.length).max)
  val zs = xs.map(_.zip(ys))
  val ls = zs.map(_.map { case (x,y) => x.padTo(y, ' ') }.mkString(" "))
  ls.mkString("\n")
}

val s = """aaa,b,cc
|a,bbbbb,c""".stripMargin

f(s)