Kara Przeczek
2008-Nov-14 20:24 UTC
[R] can I use one data frame to subset data from another?
I am new to R and have been struggling with the following problem. I apologize if there is an obvious answer that I have missed. Problem: I have a set of hourly temperature data that I would like to average over a number of different hours. Example, I would like the average temperature between 11:00 am on April 1 2008 and 12:00 pm on April 12 2008, and the average temperature between 2:00 pm on April 1 2008 and 2:00 pm on April 12 2008, and so on. I have two different data frames. The first has the air temperature and date/time data (length = 7188) the other has the start and end date/time data which I would like to average over (length = 36). name: "met_h" DateTime AT_h 09/21/2007 100 3.66850 09/21/2007 200 3.63925 09/21/2007 300 3.39800 09/21/2007 400 3.38000 09/21/2007 500 3.11425 09/21/2007 600 2.89850 09/21/2007 700 2.65600 09/21/2007 800 2.08900 09/21/2007 900 2.17325 09/21/2007 1000 3.22350 ..... name: "period" Start End 4/1/2008 11:00 4/12/2008 12:00 4/1/2008 14:00 4/12/2008 14:00 4/1/2008 17:00 4/12/2008 16:00 4/1/2008 19:00 4/12/2008 17:00 4/12/2008 13:00 4/20/2008 12:00 4/12/2008 15:00 4/20/2008 15:00 4/12/2008 17:00 4/20/2008 17:00 4/12/2008 18:00 4/20/2008 19:00 4/20/2008 13:00 4/27/2008 12:00 4/20/2008 16:00 4/27/2008 13:00 ..... I first converted the date time columns using strptime: strptime(met_h$DateTime, format="%m/%d/%Y %H:%M") I am attempting to use the second data frame to select the date to average in the first data frame: mean(met_h$AT_h[met_h$DateTime>=(period$Start) & met_h$DateTime<=(period$End)]) This gets me many error messages. Firstly because the reference data frame "period" is not the same length as the temperature data frame "met_h". However, I want to create an output of the same length as "period". I would like to use the "period" data frame to pick out certain data from the larger "met_h". Thank you very much for your time! Kara Kara Przeczek M.Sc. Candidate NRES - Environmental Science University of Northern B.C. 3333 University Way Prince George B.C V2N 4Z9 Phone: (250) 960-5427 przeczek at unbc.ca
jim holtman
2008-Nov-14 23:47 UTC
[R] can I use one data frame to subset data from another?
something like this should work;
yourMean <- lapply(seq(nrow(period)), function(.indx){
mean(met_h$AT_h[(met_h$DateTime >= period$Start[.indx]) &
(met_h$DateTime <= period$End[.indx])])
})
On Fri, Nov 14, 2008 at 3:24 PM, Kara Przeczek <przeczek at unbc.ca>
wrote:> I am new to R and have been struggling with the following problem. I
apologize if there is an obvious answer that I have missed.
>
> Problem:
> I have a set of hourly temperature data that I would like to average over a
number of different hours. Example, I would like the average temperature between
11:00 am on April 1 2008 and 12:00 pm on April 12 2008, and the average
temperature between 2:00 pm on April 1 2008 and 2:00 pm on April 12 2008, and so
on. I have two different data frames. The first has the air temperature and
date/time data (length = 7188) the other has the start and end date/time data
which I would like to average over (length = 36).
> name: "met_h"
> DateTime AT_h
> 09/21/2007 100 3.66850
> 09/21/2007 200 3.63925
> 09/21/2007 300 3.39800
> 09/21/2007 400 3.38000
> 09/21/2007 500 3.11425
> 09/21/2007 600 2.89850
> 09/21/2007 700 2.65600
> 09/21/2007 800 2.08900
> 09/21/2007 900 2.17325
> 09/21/2007 1000 3.22350
> .....
>
> name: "period"
> Start End
> 4/1/2008 11:00 4/12/2008 12:00
> 4/1/2008 14:00 4/12/2008 14:00
> 4/1/2008 17:00 4/12/2008 16:00
> 4/1/2008 19:00 4/12/2008 17:00
> 4/12/2008 13:00 4/20/2008 12:00
> 4/12/2008 15:00 4/20/2008 15:00
> 4/12/2008 17:00 4/20/2008 17:00
> 4/12/2008 18:00 4/20/2008 19:00
> 4/20/2008 13:00 4/27/2008 12:00
> 4/20/2008 16:00 4/27/2008 13:00
> .....
>
> I first converted the date time columns using strptime:
> strptime(met_h$DateTime, format="%m/%d/%Y %H:%M")
>
> I am attempting to use the second data frame to select the date to average
in the first data frame:
> mean(met_h$AT_h[met_h$DateTime>=(period$Start) &
met_h$DateTime<=(period$End)])
>
> This gets me many error messages. Firstly because the reference data frame
"period" is not the same length as the temperature data frame
"met_h". However, I want to create an output of the same length as
"period". I would like to use the "period" data frame to
pick out certain data from the larger "met_h".
>
> Thank you very much for your time!
> Kara
>
>
>
> Kara Przeczek
> M.Sc. Candidate NRES - Environmental Science
> University of Northern B.C.
> 3333 University Way
> Prince George B.C V2N 4Z9
> Phone: (250) 960-5427
> przeczek at unbc.ca
>
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem that you are trying to solve?