How should I remove the first occurrence of an object from a list in Scala?

Question

What is the best way to remove the first occurrence of an object from a list in Scala?

Coming from Java, I\'m accustomed to having a List.remove(Object o) method tha

Answer 1

This is a case where a little bit of mutability goes a long way:

def withoutFirst[A](xs: List[A])(p: A => Boolean) = {
  var found = false
  xs.filter(x => found || !p(x) || { found=true; false })
}

This is easily generalized to dropping the first n items matching the predicate. (i<1 || { i = i-1; false })

You can also write the filter yourself, though at this point you're almost certainly better off using span since this version will overflow the stack if the list is long:

def withoutFirst[A](xs: List[A])(p: A => Boolean): List[A] = xs match {
  case x :: rest => if (p(x)) rest else x :: withoutFirst(rest)(p)
  case _ => Nil
}

and anything else is more complicated than span without any clear benefits.