title: Python: Pandas - Delete the first row by group
body: <p>I have the following large dataframe (<code>df</code>) that looks like this:</p>
  
  <pre><code>    ID     date        PRICE       
  1   10001  19920103  14.500    
  2   10001  19920106  14.500    
  3   10001  19920107  14.500     
  4   10002  19920108  15.125     
  5   10002  19920109  14.500   
  6   10002  19920110  14.500    
  7   10003  19920113  14.500 
  8   10003  19920114  14.500     
  9   10003  19920115  15.000 
  </code></pre>
  
  <p><strong>Question:</strong> What's the most efficient way to delete (or remove) the first row of each ID? I want this:</p>
  
  <pre><code>        ID     date     PRICE       
      2   10001  19920106  14.500    
      3   10001  19920107  14.500     
      5   10002  19920109  14.500   
      6   10002  19920110  14.500    
      8   10003  19920114  14.500     
      9   10003  19920115  15.000 
  </code></pre>
  
  <p>I can do a loop over each unique <code>ID</code> and remove the first row but I believe this is not very efficient.</p>