title: Data frame column names after split
body: <p>When executing the following code</p>
  
  <pre><code>data &lt;- data.frame( A = c("foo", "foo", "bar", "bar"),
                      B = c("foo","bar", "foo", "bar"),
                      C = c("bla", "foo", "bla", "bar"),
                      D = c(1, 2, 3, 4 ),
                      E = c(5, 6, 7, 8 ))
  
  ds &lt;- split(data, list(data$A, data$B, data$C), drop=TRUE)
  write.table(ds[1], file="foo.csv", append=FALSE, row.names=FALSE)
  </code></pre>
  
  <p>foo.csv looks like this:</p>
  
  <pre><code> "bar.bar.bar.A","bar.bar.bar.B","bar.bar.bar.C","bar.bar.bar.D","bar.bar.bar.E"
   "bar","bar","bar",4,8
  </code></pre>
  
  <p>i.e., the column names contain the contents of the columns used to split. How do I change does names back to the original ones in a generic way? (I don't want to assign column names like "A", "B",....)</p>