title: Select rows where field is maximum, relative to another field
body: <p>I have data in the following format:</p>
  
  <p><strong>ID - Value</strong><br>
  a - 1<br>
  a - 2<br>
  a - 3<br>
  a - 4<br>
  b - 1<br>
  b - 2<br>
  b - 3<br>
  c - 1<br>
  c - 2<br>
  d - 4  </p>
  
  <p>And I would like to select rows with the maximum value for each ID, so that the output would be:</p>
  
  <p>ID  Value<br>
  a - 4<br>
  b - 3<br>
  c - 2<br>
  d - 4  </p>
  
  <p>I have tried conditioning on max(value), but am having trouble making this relative to the ID</p>