scala Remove (in place) all elements of a ListBuffer that meet a condition

Question

I have a ListBuffer. I want to remove all elements that meet a certain condition.

I could iterate over it and remove each element. But what doe Scala say about mutating a list that you are iterating over? Will it work, or will it delete the wrong elements/not return all elements? (A quick attempt with the REPL suggests that yes, it will mess up)

I could repeatedly call find and then remove the found element until I don't find any more, but that sounds inefficient.

.filter will return me a new ListBuffer without the elements, but I want to do it in place.

This

def --= (xs: TraversableOnce[A]) : ListBuffer.this.type
Removes all elements produced by an iterator from this list buffer.

looks promising but I can't quite see how to use it here

How should I do this?

Answer 1

You could combine the two and do the following:

val lb = ListBuffer(1,2,3,4,5,6)
lb --= lb.filter(_ % 2 == 0)

println(lb)
// outputs: ListBuffer(1, 3, 5)