title: Get columns by string from data.table
body: <p><code>raw</code> is a <code>data.table</code> and the following code works:</p>
  
  <pre><code>raw[,r_responseTime] #Returns the whole column
  raw[,c_filesetSize]  #Same as above, returns column
  plot(raw[,r_responseTime]~raw[,c_filesetSize]) #draws something
  </code></pre>
  
  <p>Now I want to specify these columns from a string, so for example:</p>
  
  <pre><code>col1="r_reponseTime"
  col2="c_filesetSize"
  </code></pre>
  
  <p>How can I now achieve the same as above while referencing the columns by the string?</p>
  
  <pre><code>raw[,col1] #Returns the whole column
  raw[,col2]  #Same as above, returns column
  plot(raw[,col1]~raw[,col2]) #draws something
  </code></pre>
  
  <p>Does not work, of course because I need some kind of "dereferencation". I didn't know what to search in the help and the internet, so sorry for the dumb question.</p>