title: How to aggregate every 30 minutes in R
body: <p>I am stuck in R. I need to aggregate every minute data into every 30 minutes. My data frame is like this:</p>
  
  <pre><code>    Date        Time       Power
      2008-10-11  23:57:00   0.376
      2008-10-11  23:58:00   0.374
      2008-10-11  23:59:00   0.374
      2008-10-12  0:00:00    0.334
      2008-10-12  0:01:00    0.330
  ...
      2008-12-13  19:24:00   1.390
      2008-12-13  19:25:00   1.370
      2008-12-13  19:26:00   1.368
      2008-12-13  19:27:00   1.362
      2008-12-13  19:28:00   1.352
      2008-12-13  19:29:00   1.360
  </code></pre>
  
  <p>...</p>
  
  <p>Basically, I have 500,979 rows of data for 2008. Every minute gives a power value. In order to do Time Series, I need to aggregate my data per 30 minutes. That would give me around 17,520 rows in the end. My questions are:</p>
  
  <ol>
  <li><p>Is it possible to plot time series when you have some missing values for the Power column?</p></li>
  <li><p>How to aggregate the Power value by 30 minutes please? (e.g., 0:00:00 to 0:29:00; 0:30:00 to 0:59:00)</p></li>
  </ol>
  
  <p>Thank you very much!</p>