[R] Date Time differences

[Mark R Laflamme, MD]

Greetings from an R newbie

Table imported with 4 columns containing Dates and Times, I desire to 
determine the differences between said columns
Have loaded the base and chron packages for R commander.  Have tried to 
use format but without success.  Have tried the Postix commands but 
error states "unused argument (s) (...)", even though some of the 
examples do not use (...) at the end of the command

Example:
Table is named GvY1
     Operation.Time.End      Operation.Time.Dictated   
Operation.Time.Verfiy
      7/10/2004 10:10:12         7/12/2004 9:18:03                  
7/28/2004 05:00:02

Information is mm/dd/year hh:mm:ss (time of day, e.g. the first column 
is July 10th 2004 10:10 AM at 12 seconds)
What is the best way to get the difference between any of the 2 columns? 
And eventually test statistics on the columns (eg. P values, if needed, 
but not a priority at this time)
Thanks in advance

Platform WinXP
IBM T40p
R v 1.8.1
R commander

-- 
Mark R Laflamme,MD
Regenstrief Institute	
1050 Wishard Blvd RG5
Indianapolis, IN 46202
317 630-7833