title: How to generate a sequence of dates and times with a specific start date/time in R
body: <p>I am looking to generate or complete a column of dates and times. I have a dataframe of four numeric columns and one POSIXct time column that looks like this:</p>
  
  <pre><code>    CH_1   CH_2  CH_3  CH_4           date_time
  1 -10096 -11940 -9340 -9972 2018-07-24 10:45:01
  2 -10088 -11964 -9348 -9960                &lt;NA&gt;
  3 -10084 -11940 -9332 -9956                &lt;NA&gt;
  4 -10088 -11956 -9340 -9960                &lt;NA&gt;
  5 -10084 -11944 -9332 -9976                &lt;NA&gt;
  6 -10076 -11940 -9340 -9948                &lt;NA&gt;
  7 -10088 -11956 -9352 -9960                &lt;NA&gt;
  8 -10084 -11944 -9348 -9980                &lt;NA&gt;
  9 -10076 -11964 -9348 -9976                &lt;NA&gt;
  0 -10076 -11956 -9348 -9964                &lt;NA&gt;
  </code></pre>
  
  <p>I would like to sequentially generate dates and times for the date_time column, increasing by <strong>1 second</strong> until the dataframe is filled. (i.e. the next date/time should be 2018-07-24 10:45:<strong>02</strong>). This is meant to be reproducible for multiple datasets and the number of rows that need filled is not always known, but the start date/time will always be present in that first cell.</p>
  
  <p>I know that the solution is likely within seq.Date (or similar), but the problem I have is that I won't always know the end date/time, which is what most examples I have found require. Any help would be appreciated!</p>