title: Subset dataframe based on POSIXct date and time greater than datetime using dplyr
body: <p>I am not sure what is going wrong with selecting date times as a POSIXct format. I have read several comments on subsetting a dataframe based on as.Date and I can get that to work without an issue.  I have also read many posts suggesting that filtering POSIXct formats should work, but for some reason I cannot get it to work.</p>
  
  <p>An example dataframe:</p>
  
  <pre><code>library(lubridate)
  library(dplyr)
  
  date_test &lt;- seq(ymd_hms('2016-07-01 00:00:00'),ymd_hms('2016-08-01 00:00:00'), by = '15 min')
  date_test &lt;- data.frame(date_test)
  date_test$datetime &lt;- date_test$date_test
  date_test &lt;- select(date_test, -date_test)
  </code></pre>
  
  <p>I checked that it is in POSIXct format and then tried several ways to subset the dataframe greater than 2016-07-01 01:15:00. However the output never shows the date times less than 2016-07-01 01:15:00 being removed. I am sorry if this has been asked somewhere and I cannot find it but I have looked and tried to get this to work. I am using UTC as the timezone to avoid daylight savings time issues so that is not the issue here - unless the filter requires it.</p>
  
  <pre><code>class(date_test$datetime)
  
  date_test &lt;- date_test %&gt;% filter(datetime &gt; '2016-07-01 01:15:00')
  
  date_test &lt;- date_test %&gt;% 
    filter(datetime &gt; as.POSIXct("2016-07-01 00:15"))
  
  date_test &lt;- subset(date_test, datetime &gt; as.POSIXct('2016-07-01 01:15:00')) 
  </code></pre>
  
  <p>Now if I filter using:</p>
  
  <pre><code>date_test &lt;- date_test %&gt;% 
    filter(datetime &gt; as.POSIXct("2016-07-10 01:15:00"))
  </code></pre>
  
  <p>the output is very strange with a day behind and the wrong time?</p>
  
  <pre><code>2016-07-09 13:30:00
  2016-07-09 13:45:00
  2016-07-09 14:00:00
  2016-07-09 14:15:00
  2016-07-09 14:30:00
  </code></pre>
  
  <p>If it helps I am using MAC OS Sierra with R Studio Version 1.0.143 and R You Stupid Darkness, DPLYR 0.5 and Lubridate 1.6</p>