Is it possible to Merge stacks with LINQ

Question

I'm just starting to learn LINQ, I'm wondering if it would be possible to group the elements in 3 different stacks using LINQ. this is what I have, could it be possible to add more than one array in the from clause, and how?

        var uniqueValues =
            from n in valuesStack.ToArray()
            group n by n into nGroup
            select nGroup.Key;

Answer 1

This is untested:

var uniqueValues =
    from stack in stacks
    from n in stack
    group n by n into nGroup
    select nGroup.Key;

Answer 2

You can Union the stacks together.

var s1 = new Stack<int>();
var s2 = new Stack<int>();
var s3 = new Stack<int>();
var r = s1.Union(s2.Union(s3)).ToArray();

Answer 3

var uniqueValues = stack1
    .Concat(stack2)
    .Concat(stack3)
    .Distinct();

or you could use Union:

var uniqueValues = stack1
    .Union(stack2)
    .Union(stack3);