Subtract HashSets (and return a copy)?

c# hashset
mpen picture mpen · Oct 9, 2010 · Viewed 10.4k times · Source

I've got a HashSet,

var universe = new HashSet<int>();

And a bunch of subsets,

var sets = new List<HashSet<int>>(numSets);

I want to subtract a chunk, which I can do like this:

var remaining = universe.ExceptWith(sets[0]);

But ExceptWith works in-place. I don't want to modify the universe. Should I clone it first, or is there a better way?

Answer

Thomas Levesque picture Thomas Levesque · Oct 9, 2010

I guess I should clone it first? How do I do that?

var universe = new HashSet<int>();
var subset = new HashSet<int>();
...

// clone the universe
var remaining = new HashSet<int>(universe);
remaining.ExceptWith(subset);

Not as simple as with the Except extension method, but probably faster (you should run a few performance tests to make sure)

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