title: how to gather columns which are numbered sequentially with tidyr
body: <p>I have a set of columns as follows</p>
  
  <pre><code>rowid   TimePoint2   TimePoint3    TimePoint4     TimePoint5    TimePoint6
  </code></pre>
  
  <p>I want to tidy the data but the gather function doesn't recognise the column names when I use he paste function
  What I want is</p>
  
  <pre><code>rowid
  1   TimePoint2    43
  2   TimePoint3    34
  3   TimePoint4    24
  4   TimePoint5    22
  5   TimePoint6    44
  </code></pre>
  
  <p>etc</p>
  
  <p>My code:</p>
  
  <p>so instead of writing:</p>
  
  <pre><code>y="TimePoint"
    Mydf&lt;-
      select(df,matches(y),rowid)%&gt;%
      gather(variable, value, TimePoint1,TimePoint2,TimePoint3,TimePoint4,TimePoint5,TimePoint6)
  </code></pre>
  
  <p>I want to write something like: </p>
  
  <pre><code>y="TimePoint"
    Mydf&lt;-
      select(df,matches(y),rowid)%&gt;%
      gather(variable, value, paste(y,1:10,",",sep=""))
  </code></pre>
  
  <p>The error I get with the above is <code>Error: All select() inputs must resp;ve to integer column positions. The following do not: * paste (y,1:10,",",sep="")</code></p>