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 [EMAIL PROTECTED] ______________________________________________ R-help@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.
