title: R; Time series analysis on sensor data
body: <p>I have a data frame of sensor data</p>
  
  <p>I have a data frame as follows:</p>
  
  <pre><code>pressure    datetime
  4.848374    2016-04-12 10:04:00   
  4.683901    2016-04-12 10:04:32   
  5.237860    2016-04-12 10:13:20 
  </code></pre>
  
  <p>Now, I would like to apply <code>ARIMA</code> to make predictive analytics.</p>
  
  <p>Since the data is not sampled uniformly, I have aggregated it on Hourly basis which looks as follows:</p>
  
  <pre><code>datetime                    pressure
  "2016-04-19 00:00:00 BST"   5.581806
  "2016-04-19 01:00:00 BST"   4.769832
  "2016-04-19 02:00:00 BST"   4.769832  
  "2016-04-19 03:00:00 BST"   4.553711  
  "2016-04-19 04:00:00 BST"   6.285599  
  "2016-04-19 05:00:00 BST"   5.873414
  </code></pre>
  
  <p>The pressure for every hour looks like below:</p>
  
  <p><a href="https://i.stack.imgur.com/ATmPq.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ATmPq.png" alt="enter image description here"></a></p>
  
  <p>But I can't create <code>ts</code> object as I am not sure what the frequency should be for Hourly data. </p>