title: What does the !! operator mean in R, particularly in the context !!sym("x")
body: <p>What does "!!" do in R, and why would you use it?</p>
  
  <p>Specifically, I'm looking at a function that involves the phrase
  <code>a = !!sym("x")</code> where <code>"x"</code> is a string. I thought <code>sym</code> worked by turning a string into an object, so <code>a = sym("x")</code> would set <code>a</code> equal to the object <code>x</code>. What is the <code>!!</code> there for? I read that it unquotes whatever is after it, but I thought <code>sym</code> itself unquoted strings?</p>
  
  <p>I also see <code>!!</code> used with other functions. What is it doing?</p>