title: Find last id and increment values in pandas dataframe
body: <p>I have a dataframe with values as such:</p>
  
  <pre><code>╔════╦═════════╦══════╦═══════╗
  ║ id ║ quarter ║ year ║ value ║
  ╠════╬═════════╬══════╬═══════╣
  ║  1 ║       4 ║ 2017 ║     5 ║
  ║  1 ║       1 ║ 2018 ║     7 ║
  ║  2 ║       1 ║ 2018 ║     8 ║
  ╚════╩═════════╩══════╩═══════╝
  </code></pre>
  
  <p>I want to find the last id and increment the quarters to 4 whilst keeping the same value. The expected output is:</p>
  
  <pre><code>╔════╦═════════╦══════╦═══════╗
  ║ id ║ quarter ║ year ║ value ║
  ╠════╬═════════╬══════╬═══════╣
  ║  1 ║       4 ║ 2017 ║     5 ║
  ║  1 ║       1 ║ 2018 ║     7 ║
  ║  1 ║       2 ║ 2018 ║     7 ║
  ║  1 ║       3 ║ 2018 ║     7 ║
  ║  1 ║       4 ║ 2018 ║     7 ║
  ║  2 ║       1 ║ 2018 ║     8 ║
  ║  2 ║       2 ║ 2018 ║     8 ║
  ║  2 ║       3 ║ 2018 ║     8 ║
  ║  2 ║       4 ║ 2018 ║     8 ║
  ╚════╩═════════╩══════╩═══════╝
  </code></pre>
  
  <p>I have tried using df.last() in pandas to find the last instance of the id and increment the quarters through a loop but it does not seem to work. I am new to python and pandas so any suggestions would be great.</p>