title: Aggregate in time intervals
body: <p>I want to analyze some measurment data in R</p>
  
  <pre><code>&gt; head(data)
                   Time     Val
  1 2011-12-01 10:11:21      20
  2 2011-12-01 10:11:24       0
  3 2011-12-01 10:11:24      30
  4 2011-12-01 10:11:25       0
  5 2011-12-01 10:11:29      80
  6 2011-12-01 10:13:31       0
  </code></pre>
  
  <p>I experimented both with Zoo and with as.Date, but none of them led to an answer to the following questions:</p>
  
  <ol>
  <li>How can I plot a histogram per minute over the 24 hours of the day?</li>
  <li>How can I calculate and plot the mean value for each day (not day of month but day single day)?</li>
  </ol>