R help - Jul 2005 - Where to learn how to deal with time class variable?

Dear R-helpers,
  In my data set, I have a time variable 'RecordTime'
whose class property is 'times'. When I list my data
set, I see the values of RecordTime is like 10:20:30
in a 'h:m:s' format. Suppose I want to choose all the
data after 10 o'clock, then use

subset(data,RecordTime>10:20:30)

just doesn't work. I noticed that all the values of
RecordTime seem to take some decimals when using
str(data). But how can I easily find the
correspondence between those decimals and the exact
times? I have looked at the help file of POSIXlt and
related functions. Yet I couldn't find any useful
instruction on this issue.

On 7/17/05, Kerry Bush <kerryrekky at yahoo.com>
wrote:
> Dear R-helpers,
>  In my data set, I have a time variable 'RecordTime'
> whose class property is 'times'. When I list my data
> set, I see the values of RecordTime is like 10:20:30
> in a 'h:m:s' format. Suppose I want to choose all the
> data after 10 o'clock, then use
> 
> subset(data,RecordTime>10:20:30)
> 
> just doesn't work. I noticed that all the values of
> RecordTime seem to take some decimals when using
> str(data). But how can I easily find the
> correspondence between those decimals and the exact
> times? I have looked at the help file of POSIXlt and
> related functions. Yet I couldn't find any useful
> instruction on this issue.
Are you using the chron library?  Assuming that is the case, you
want to make sure that the object you are comparing your times
object to is also a times object:
> library(chron)
> example(chron) # this defines a times object tms (output omitted)
> tms
[1] 23:03:20 22:29:56 01:03:30 18:21:03 16:56:26
> subset(tms, tms > times("20:00:00"))
[1] 23:03:20 22:29:56