Picking 2 random elements from array

Question

What is the most efficient way to select 2 unique random elements from an array (ie, make sure the same element is not selected twice).

I have so far:

Answer 1

http://underscorejs.org/#sample

_.sample(list, [n])

Produce a random sample from the list. Pass a number to return n random elements from the list. Otherwise a single random item will be returned.

_.sample([1, 2, 3, 4, 5, 6]);
=> 4

_.sample([1, 2, 3, 4, 5, 6], 3);
=> [1, 6, 2]

Looking at the source it uses shuffle just like @thg435 suggested.