title: Create a time interval of 15 minutes from minutely data in R?
body: <p>I have some data which is formatted in the following way: </p>
  
  <pre><code>time     count 
  00:00    17
  00:01    62
  00:02    41
  </code></pre>
  
  <p>So I have from 00:00 to 23:59hours and with a counter per minute. I'd like to group the data in intervals of 15 minutes such that:</p>
  
  <pre><code>time           count
  00:00-00:15    148   
  00:16-00:30    284
  </code></pre>
  
  <p>I have tried to do it manually but this is exhausting so I am sure there has to be a function or sth to do it easily but I haven't figured out yet how to do it.</p>
  
  <p>I'd really appreciate some help!! </p>
  
  <p>Thank you very much!</p>