[R] subset a data.frame

[David Winsemius]

On Nov 2, 2010, at 11:53 AM, Simone Gabbriellini wrote:

> Hello List,
>
> this should be simple, but cannot figure it out. I am trying to  
> subset a data.frame like this:
>
>> data4
>       users                time
> 1      user5 	2009-12-01 14:09:58
> 2      user1 	2009-12-01 14:40:16
> 3      user8 	2009-12-04 08:18:37
> 4      user6 	2009-12-04 08:18:37
> 5     user83	2009-12-04 08:18:37
> 6     user82 	2009-12-04 08:18:37
> 7     user31 	2009-12-04 08:18:37
> 8     user85 	2009-12-04 08:18:37
> 9     user33 	2009-12-04 08:18:37
> 10     user2 	2010-01-05 07:18:36
>
> I would like to subset it and retain, let's say, only the data with  
> time < '2010-01-05 07:18:36', but I have no idea about the sintax to  
> do that.
>
> is something like this close to the correct way:
>
> active<-data4['time'<= as.POSIXct("2010-01-05 07:18:36",  
> origin="1970-01-01 00:00:00-00")]

Close. Try:

  active <- data4[data4$time <= as.POSIXct("2010-01-05 07:18:36",  
origin="1970-01-01 00:00:00-00") , ]

Or:

active <- subset(data4, time <= as.POSIXct("2010-01-05 07:18:36",  
origin="1970-01-01 00:00:00-00") )

>


--

David Winsemius, MD
West Hartford, CT