title: Deleting elements that appear only once in a list of vectors in R
body: <p>I have a list of 3 vectors, <code>X</code>, <code>Y</code>, and <code>Z</code>. I was wondering how I could <strong>delete</strong> elements that appear only once (here <code>ChandlerA</code> and <code>Trus.Hsu</code>) across all 3 vectors?</p>
  
  <pre><code>d = list(X = c(Bit.KnoA = 4, Bit.KnoB = 1, Bit.KnoC = 2, ChandlerA = 3, Ellis.etal =4, 
                 Mubarak=5, SheenA=6,  Shin.Ellis=7 , Sun = 8, Trus.Hsu=3 ), 
  
           Y = c(Bit.KnoA = 6, Bit.KnoB = 3, Bit.KnoC = 4, Ellis.etal =1, Mubarak=2, 
                SheenA=1,  Shin.Ellis=2 , Sun = 1),
  
           Z = c(Bit.KnoB = 2) )
  </code></pre>