title: Remove first value from multiple timeseries in a pandas dataframe
body: <p>I have a dataframe with some telemetry data for multiple devices. Every row has device ID and a timestamp and some other fields. I want to remove the first, that is earliest, entry for every device. How would I go about it?</p>
  
  <p>For example, my data might look like this</p>
  
  <pre><code>timestamp,        device id, val1, val2, val3
  2018-01-02 18:01  123        0     1     1
  2018-01-02 18:05  124        1     3     2
  2018-01-02 18:06  123        4     5     5
  2018-01-02 18:02  125        2     7     2
  2018-01-02 18:07  124        6     2     2
  </code></pre>
  
  <p>And I want to remove the earliest entry for device 123, earliest for device 124 and earliest for device 125 (even if it is the only one)</p>