How to generate the power set of a set in Scala

Question

I have a Set of items of some type and want to generate its power set.

I searched the web and couldn't find any Scala code that adresses this specific task.

This is what I came up with. It allows you to restrict the cardinality of the sets produced by the length parameter.

def power[T](set: Set[T], length: Int) = {    var res = Set[Set[T]]()    res ++= set.map(Set(_))     for (i <- 1 until length)       res = res.map(x => set.map(x + _)).flatten     res    } 

This will not include the empty set. To accomplish this you would have to change the last line of the method simply to res + Set()

Any suggestions how this can be accomplished in a more functional style?

Answer 1

Looks like no-one knew about it back in July, but there's a built-in method: subsets.

scala> Set(1,2,3).subsets foreach println Set() Set(1) Set(2) Set(3) Set(1, 2) Set(1, 3) Set(2, 3) Set(1, 2, 3)