title: Generate permutations of specific length with repetition in R?
body: <p>I have a list of words and I need to generate all the permutations with repetition. The length of permutation must be specified. The words list is quite big(i.e.  30 words) so the function I needs to be efficient too.. 
    Example: </p>
  
  <pre><code>wordsList = c("alice", "moon", "walks", "mars", "sings", "guitar", "bravo")
  </code></pre>
  
  <p>I need to generate all the permutations given that each permutation must have exactly 3 words.  That would be <code>["alice", "moon", "walks"]</code>, <code>["alice", "walks", "moon"]</code>, <code>["moon", "alice", "walks"]</code>  etc</p>