Greetings,

My data set has dates and times that I am working with.  Some of the times
in Time_of_end are blank.  This is supposed to dictate that the particular
experiment lasted 48 hours.  I would like to add 48 hours to the start
Start_of_Experiment for another column as End_of_Experiment including both
the ones with 48 added and those with early times.  I was thinking
something with a conditional statement but I can't seem to figure out what
code to use.  Any insight would be appreciated.  Let me know if there is
anything else you need.  Thanks for your time.

I have Start_of_Experiment in POSIX format for time calculations from the
following:

data$Start_of_Experiment=as.POSIXct(strptime(data$start_time, "%m/%d/%Y
%H:%M:%S"))

Here is a subset of my data.

        ID        group Start_date Time_of_experiment Time_of_end
1    20209         4    02/02/2009           12:38:00
26   30209         3   03/02/2009           12:40:00      13:32:00
27   31609         4   03/16/2009           11:28:00      12:26:00
28   40609         4   04/06/2009           11:17:00
53   42709         4   04/27/2009           11:15:00       9:30:00
76   51109         3   05/11/2009           11:51:00
101  51809         1  05/18/2009           12:28:00
126  62209         3  06/22/2009           11:31:00
150  71309         4  07/13/2009           12:12:00      13:37:00
173  81009         4  08/10/2009           11:32:00      20:52:00
    Start_of_Experiment
1   2009-02-02 12:38:00
26  2009-03-02 12:40:00
27  2009-03-16 11:28:00
28  2009-04-06 11:17:00
53  2009-04-27 11:15:00
76  2009-05-11 11:51:00
101 2009-05-18 12:28:00
126 2009-06-22 11:31:00
150 2009-07-13 12:12:00
173 2009-08-10 11:32:00

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