title: Add extra rows in a data frame according to a list
body: <p>I have a dataframe such as </p>
  
  <pre><code>SP_names    Gp1 Gp2 Gp3 Gp4
  Sp1 0   0   1   1
  Sp2 0   1   1   1
  Sp3 1   1   2   3
  Sp4 1   3   6   1
  Sp5 0   2   0   2
  </code></pre>
  
  <p>and a list such as :</p>
  
  <pre><code>list&lt;-c("Sp1","Sp2","Sp3","Sp4","Sp5","Sp6","Sp7")
  </code></pre>
  
  <p>and the idea is that for each element in the list that are not present in the SP_names, I want to add a row (so fo <code>Sp6</code> and <code>Sp7 filled by 0</code>) and get: </p>
  
  <pre><code>SP_names    Gp1 Gp2 Gp3 Gp4
  Sp1 0   0   1   1
  Sp2 0   1   1   1
  Sp3 1   1   2   3
  Sp4 1   3   6   1
  Sp5 0   2   0   2
  Sp6 0   0   0   0
  Sp7 0   0   0   0
  </code></pre>
  
  <p>Have you an idea with R?</p>