title: How can I gather_ on all columns but one?
body: <p>I need to <code>gather_</code> on all columns of a dataframe, except for one. Example:</p>
  
  <pre><code># I want to generate a dataframe whose column names are the letters of the alphabet. If you know of a simpler way, let me know!
  foo &lt;- as.data.frame(matrix(runif(100), 10, 10))
  colnames(foo) &lt;- letters[1:10]
  </code></pre>
  
  <p>Now, suppose I want to gather on all columns except column <code>e</code>. This won't work:</p>
  
  <pre><code>mycol &lt;- "e"
  foo_melt &lt;- gather_(foo, key = "variable", value = "value", -mycol)
  #Error in -mycol : invalid argument to unary operator
  </code></pre>
  
  <p>This will:</p>
  
  <pre><code>column_list &lt;- colnames(foo)
  column_list &lt;- column_list[column_list != mycol]
  foo_melt &lt;- gather_(foo, key = "variable", value = "value", column_list)
  </code></pre>
  
  <p>Looks quite convoluted if you ask me. Isn't there any simpler way?</p>