title: NA value when using strptime() to convert from 12 hr format to 24 hr format in R
body: <p>I have a data frame with a column of dates/times in a 12 hour timestamp format (<code>mm/dd/yyyy hh:mm:ss AM/PM</code>). I would like to change these to a 24 hour/ military time format (<code>mm/dd/yyyy hh:mm:ss</code>).</p>
  
  <p>I have tried using <code>strptime(times, "%m/%d/%Y %I:%M:%S %p")</code>. This works for the majority of the rows in the column, but some are returning <code>NA</code>. I went and looked at the original 12 hour time for the rows returning <code>NA</code> and they are a correct date format, and the same as the rest. I am not sure why I am getting <code>NA</code> for some of the values, or how to fix this error.</p>
  
  <p>Anyone know why I am getting <code>NA</code> values and how to fix it?
  Thanks!</p>
  
  <p>Update: I've noticed that all the dates that are returning <code>NA</code> either contain 2 AM or 2 PM. I'm not sure why that would be causing an issue though.</p>