title: How to get the first date from a vector?
body: <p>I have a vector of POSIXct objects, I would like to determine the first and the last date/time value in the list.</p>
  
  <pre><code>POSIXct_vector &lt;- read.csv(file="data", as.is=TRUE)
  POSIXct_vector$DateTime &lt;- as.POSIXct(POSIXct_vector)
  
  #returns NA
  min(POSIXct_vector$DateTime)
  
  #returns NA
  max(POSIXct_vector$DateTime)
  </code></pre>