title: Aggregating hourly data into daily aggregates
body: <p>I have an hourly weather data in the following format:</p>
  
  <pre><code>Date,DBT
  01/01/2000 01:00,30
  01/01/2000 02:00,31
  01/01/2000 03:00,33
  ...
  ...
  12/31/2000 23:00,25
  </code></pre>
  
  <p>What I need is a daily aggregate of max, min, ave like this:</p>
  
  <pre><code>Date,MaxDBT,MinDBT,AveDBT
  01/01/2000,36,23,28
  01/02/2000,34,22,29
  01/03/2000,32,25,30
  ...
  ...
  12/31/2000,35,9,20
  </code></pre>
  
  <p>How to do this in R?</p>