title: How do I count the number of observations at given intervals in R?
body: <p>I have data which includes variables for the hour, the minute, and the second for each observation. I want to count the number of observations before 3am, all observations before 6am,  all observations before 9am and so on. Any help on this would be hugely appreciated.</p>
  
  <p>Example of the data:</p>
  
  <pre><code>day    hour    minute   second
  01       17        10       03
  01       17        14       20
  01       17        25       27
  01       17        32       39
  01       17        33       40
  01       17        34       10
  01       17        34       14
  01       17        34       16
  01       17        34       21
  01       17        34       23
  01       17        34       25
  01       17        34       31
  01       17        34       36
  </code></pre>
  
  <p>I have about 300,000 observations like this. </p>
  
  <p>hour  : int  17 17 17 17 17 17 17 17 17 17  </p>
  
  <p>minute: int  10 14 25 32 33 34 34 34 34 34  </p>
  
  <p>second: int  3 20 27 39 40 10 14 16 21 23</p>