[R] Subset a datafram according to time

[MacQueen, Don]

(apologies in advance for the stupid line-wrapping that I expect my email
software to force upon us)

If I understand correctly what you want, I would

(1) in both data frames, combine date and time into a single column
(variable) that is class POSIXct

(2) use the merge() function

This assumes that your every-6-minutes data frame does NOT have a column
with the same name as the observations in the every-second data frame. In
fact, it would be best if the only column name they have in common is the
date-time column.

Your question is a little puzzling because your example data is not one
obs per second, nor is it one per every 6 minutes.

This may help:
 as.POSIXct('01/12/2012 03:14:55', format='%m/%d/%Y %H:%M:%S')

or perhaps

 mydat$dt <- as.POSIXct( paste(mydat$date,mydat$time) , format='%m/%d/%Y
%H:%M:%S')

(supposing that your data frame is named mydat, and it has columns named
'date' and 'time' that look like those in your example.)

-Don


-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 2/9/12 1:22 AM, "NickNz125" <nickthomas125 at gmail.com> wrote:

>PREFERED WAY OF DOING IT
>I have a data set of observations every second for a month long period, I
>want to extract the observations according to the  date & time of another
>data frame ( the other data frame is in the same format). I want to do
>this
>to match these  observations   to my test observations (in the other data
>frame) which are done every 6 minutes. So basically im shrinking the data
>frame of second observations to only display the date time observation
>every
>6 minutes.
>
>ALTERNATIVE WAY
>In other words I just wanna extract every 6 minute observation value from
>this dataframe of everysecond observations
>
>date                time            observations
>02/08/2011 00:00	 1.165	
>02/08/2011 00:01	 1.241
>02/08/2011 00:02	 1.232
>
>
>Im pretty new to the porgram done 2 days on it learning and learning, im
>getting my head around it.
>
>Help would be much appreciated.
>
>--
>View this message in context:
>http://r.789695.n4.nabble.com/Subset-a-datafram-according-to-time-tp437229
>3p4372293.html
>Sent from the R help mailing list archive at Nabble.com.
>
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