title: dplyr "Select" - Error: found duplicated column name
body: <p>I am trying to extract columns from a DT to a new DT using select{dplyr}</p>
  
  <pre><code>extract_Data &lt;- select(.data = master_merge, subjectID, activity_ID,
                             contains("mean\\(\\)"), contains("std\\(\\)"))
  </code></pre>
  
  <p>There are 563 columns so I am asking to extract the first and second column (subject, activity) and all other columns where mean() or std() is present. </p>
  
  <p>There are NO duplicate columns that can be created here. so stumped as to the why. I have tried every variation of select but always Error: Duplicated Column name.</p>
  
  <p>How can I troubleshoot this - I have gone through all 563 columns names and there are no duplicates. </p>