title: Repeat the rows in a data frame based on values in a specific column
body: <p>I would like to repeat entire rows in a data-frame based on the <code>samples</code> column.</p>
  
  <p>My input:</p>
  
  <pre><code>df &lt;- 'chr start end samples
          1   10   20    2
          2   4    10    3'
  df &lt;- read.table(text=df, header=TRUE)
  </code></pre>
  
  <p>My expected output:</p>
  
  <pre><code>df &lt;- 'chr start end  samples
          1   10   20   1-10-20-s1
          1   10   20   1-10-20-s2
          2   4    10   2-4-10-s1
          2   4    10   2-4-10-s2
          2   4    10   2-4-10-s3'
  </code></pre>
  
  <p>Some idea how to perform it wisely?</p>