title: Multiple unions
body: <p>I am trying to do unions on several lists (these are actually GRanges objects not integer lists but the priciple is the same), basically one big union.</p>
  
  <pre><code>x&lt;-sort(sample(1:20, 9))
  y&lt;-sort(sample(10:30, 9))
  z&lt;-sort(sample(20:40, 9))
  mylists&lt;-c("x","y","z")
  emptyList&lt;-list()
  sapply(mylists,FUN=function(x){emptyList&lt;-union(emptyList,get(x))})
  </code></pre>
  
  <p>That is just returning the list contents.
  I need the equivalent of </p>
  
  <pre><code>union(x,union(y,z))
  [1]  2  3  5  6  7 10 13 15 20 14 19 21 24 27 28 29 26 31 36 39
  </code></pre>
  
  <p>but written in an extensible and non-"variable explicit" form</p>