Hi Stefano, I might be missing something, but try this: MteBove<-read.table(text="posix_date posix_time snow temp 2010-01-19 23:30:00 45 NA 2010-01-20 00:30:00 10 2.7 2010-01-20 03:00:00 45 NA 2010-01-20 03:30:00 44 NA 2010-01-20 04:00:00 44 NA 2010-01-20 04:30:00 44 NA 2010-01-20 05:00:00 44 NA 2010-01-20 05:30:00 45 NA 2010-01-20 06:00:00 44 NA 2010-01-20 06:30:00 45 NA 2010-01-20 23:30:00 45 NA 2010-01-21 00:30:00 10 2.7 2010-01-21 03:00:00 45 NA 2010-01-21 03:30:00 44 NA 2010-01-21 04:00:00 44 NA 2010-01-21 04:30:00 44 NA 2010-01-21 05:00:00 44 NA 2010-01-21 05:30:00 45 NA 2010-01-21 06:00:00 44 NA 2010-01-21 06:30:00 45 NA", header=TRUE) MteBove$day<-as.Date(MteBove$posix_date,"%Y-%m-%d") by(MteBove$snow,MteBove$day,mean)
and if you have NA values, add na.rm=TRUE to the last line. Jim On Tue, Jun 7, 2016 at 4:55 PM, Stefano Sofia <stefano.so...@regione.marche.it> wrote: > Dear R-list users, > I have the following data frame, called MteBove: > > posix_date snow temp > ... > 2010-01-20 23:30:00 45 NA > 2010-01-02 00:30:00 10-2.7 > 2010-01-20 03:00:00 45 NA > 2010-01-20 03:30:00 44 NA > 2010-01-20 04:00:00 44 NA > 2010-01-20 04:30:00 44 NA > 2010-01-20 05:00:00 44 NA > 2010-01-20 05:30:00 45 NA > 2010-01-20 06:00:00 44 NA > 2010-01-20 06:30:00 45 NA > ... > >> sapply(MteBove, class) > gives > $posix_date > [1] "POSIXct" "POSIXt" > > $snow > [1] "numeric" > > $temp > [1] "numeric" > > There are semi-hourly data (i.e. 48 data each day) from the first of November > to the first of May of each Winter season, and I need the daily mean for snow > and temp. > First I created a subset for each Winter season > I tried to create a new column with only the day, like > >> MteBove$day <- trunc(MteBove$posix_date, "days") > > and then > >> list_days <- unique(MteBove$day) >> means <- rapply(list_days, function(x) mean(MteBove[MteBove$day == x, ], >> na.rm=T)) > > with the following result: > [1] "means IS" > sec min hour mday mon year wday yday isdst > NA NA NA NA NA NA NA NA NA > > I tried some changes always in this direction, with no success. > Is there an efficient way to do that? > Could somebody give me an hint about it? > > Thank you for your attention and your help > Stefano Sofia > > > ________________________________ > > AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere > informazioni confidenziali, pertanto è destinato solo a persone autorizzate > alla ricezione. I messaggi di posta elettronica per i client di Regione > Marche possono contenere informazioni confidenziali e con privilegi legali. > Se non si è il destinatario specificato, non leggere, copiare, inoltrare o > archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, > inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio > computer. Ai sensi dell’art. 6 della DGR n. 1394/2008 si segnala che, in caso > di necessità ed urgenza, la risposta al presente messaggio di posta > elettronica può essere visionata da persone estranee al destinatario. > IMPORTANT NOTICE: This e-mail message is intended to be received only by > persons entitled to receive the confidential information it may contain. > E-mail messages to clients of Regione Marche may contain information that is > confidential and legally privileged. Please do not read, copy, forward, or > store this message unless you are an intended recipient of it. If you have > received this message in error, please forward it to the sender and delete it > completely from your computer system. > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
