title: Determining whether values between rows match for certain columns
body: <p>I am working with some observation data and have run into a bit of an issue beyond my current capabilities. I surveyed different polygons (the column &quot;PolygonID&quot; in the screenshot) for lizards two times during a survey season. I want to determine the total search effort (shown in the column &quot;Effort&quot;) for each individual polygon within each survey round. Problem is, the software I was using to collect the data sometimes creates unnecessary repeats for polygons within a survey round. There is an example of this in the screenshot for the rows with PolygonID P3.</p>
  <p>Most of the time it does not affect the effort calculations because the start and end time for the rows (the fields used to calculate effort) are the same, and I know how to filter the dataset so it only shows one line per polygon per survey, but I have reason to be concerned there might be some lines where the software glitched and assigned incorrect start and end times for one of the repeat lines. Is there a way I can test whether start and end time match for any such repeats with R, rather than manually going through all the data?</p>
  <p>Thank you!</p>
  <p><a href="https://i.stack.imgur.com/i1zZl.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/i1zZl.jpg" alt="enter image description here" /></a></p>