title: Split data frame by same value/text and then merge vertically
body: <p>I have data frame <code>df</code> as following:</p>
  
  <pre><code> df$x1    df$x2     df$x3    df$x4     df$x5    df$x6          
   Acti     Acti     Arthrex  Arthrex    Aflac    Aflac     
    4         5        3         1        2         5
    1         3        5         2        1         4        
  </code></pre>
  
  <p>I wish to split the data frame by text in first row and then merge vertically. My desired output would be like following:</p>
  
  <pre><code> df$x1    df$x2           
   Acti     Acti         
    4         5     
    1         3     
   Arthrex  Arthrex
    3         1
    5         2
   Aflac    Aflac
    2         5
    1         4 
  </code></pre>
  
  <p>Many thanks for your help. </p>