title: R - How to re-order row index number
body: <p>Simply put, I have the following data frame:</p>
  
  <pre><code>        Signal
      4   9998
      3   549
      1   18
      5   2.342
      2   0.043
  </code></pre>
  
  <p>and I want to reset the index numbers to be like :</p>
  
  <pre><code>        Signal
      1   9998
      2   549
      3   18
      4   2.342
      5   0.043
  </code></pre>