title: Extracting common character strings from multiple vectors of different lengths
body: <p>Is there function in R to find the common characters in multiple vectors (of different lengths). For example, if I have 3 vectors...</p>
  
  <pre><code> a1 &lt;- LETTERS[1:7]
   a2 &lt;- LETTERS[4:8]
   a3 &lt;- LETTERS[2:10]
  
  a1
  # [1] "A" "B" "C" "D" "E" "F" "G"
  a2
  # [1] "D" "E" "F" "G" "H"
  a3
  # [1] "B" "C" "D" "E" "F" "G" "H" "I" "J"
  </code></pre>
  
  <p>I can think of a messy solutions...</p>
  
  <pre><code>intersect(intersect(a1,a2),a3)
  # [1] "D" "E" "F" "G"
  </code></pre>
  
  <p>Problem is, I have around 8 or 9 vectors. Is there a better way to this?</p>