title: R add specific (different) amounts of times to entire column
body: <p>I have a table in R like:</p>
  
  <pre><code>start                duration
  02/01/2012 20:00:00  5
  05/01/2012 07:00:00  6
  etc...               etc...
  </code></pre>
  
  <p>I got to this by importing a table from Microsoft Excel that looked like this:</p>
  
  <pre><code>date        time      duration
  2012/02/01  20:00:00  5
  etc...
  </code></pre>
  
  <p>I then merged the date and time columns by running the following code:</p>
  
  <pre><code>d.f &lt;- within(d.f, { start=format(as.POSIXct(paste(date, time)), "%m/%d/%Y %H:%M:%S") })
  </code></pre>
  
  <p>I want to create a third column called 'end', which will be calculated as the number of hours after the start time. I am pretty sure that my time is a POSIXct vector. I have seen how to manipulate one datetime object, but how can I do that for the entire column?</p>
  
  <p>The expected result should look like:</p>
  
  <pre><code>start                duration  end
  02/01/2012 20:00:00  5         02/02/2012 01:00:00
  05/01/2012 07:00:00  6         05/01/2012 13:00:00
  etc...               etc...    etc...
  </code></pre>