title: Convert numbers to letters
body: <p>I have the following vector:</p>
  
  <pre><code>x &lt;- c(11, 12, 21, 22)
  </code></pre>
  
  <p>And I want to convert it to the corresponding letters, i.e., I want to get this result:</p>
  
  <pre><code>AA AB BA BB
  </code></pre>
  
  <p>How do I make this? I bet there's a simple answer and that it goes through using the reserved <code>LETTERS</code> vector, but I can't figure out a solution. This is the best I've managed to come up with so far (you might want to take the kids out of the room):</p>
  
  <pre><code>&gt; paste0(gsub(1, LETTERS[1], substr(x, 1, 1)),
           gsub(2, LETTERS[2], substr(x, 1, 1)))
  [1] "A1" "A1" "2B" "2B"
  </code></pre>