title: how do you pick the hour, minute and second from the posixct formated datetime in R
body: <p>I have a data frame like this:</p>
  
  <pre><code>dput(tail(x,10))
  structure(list(DATE = structure(c(1375725600, 1375729200, 1375732800, 
  1375736400, 1375740000, 1375743600, 1375747200, 1375750800, 1375754400, 
  1375758000), class = c("POSIXct", "POSIXt"), tzone = ""), VOLUME = c(2790797L, 
  2670868L, 2586397L, 2470043L, 2336334L, 2228206L, 2129270L, 2032518L, 
  872133L, 725377L), PC = c(10.12, 9.95, 9.9, 9.46, 8.99, 8.94, 
  9.79, 8.45, 8.85, 8.5)), .Names = c("DATE", "VOLUME", "PC"), row.names = 3399:3408, class = "data.frame")
  </code></pre>
  
  <p>I need to create another colume for time so that I can pick and choose between different times in a day.</p>
  
  <p>I have tried this:</p>
  
  <pre><code>x$time&lt;-format(x$DATE, "%H:%M:%S)
  </code></pre>
  
  <p>did not work, I am getting empty values.</p>
  
  <p>I also tried this:</p>
  
  <pre><code>x$t&lt;-strptime(x$DATE, format="%H:%M:%S") 
  </code></pre>
  
  <p>I get NA values. My x$DATE is formated as POSIXct, any ideas what might me going on here?</p>