Hi
r-help-boun...@r-project.org napsal dne 05.03.2009 09:46:17: > I am fairly new to R and I would like to do the following, but do not know > where to start. Any help or direction would be appreciated. > I have a time series of snow depth measurements. I would like to determine the > depth of snowfall for each snowfall event. There is noise in the data so I > only want to add data values if the subsequent depth is greater than the > previous by a certain margin. I am only interested in calculating snow > accumulation events. > Example data: > > Time depth > 1 84.3 > 2 84.5 > 3 86 > 4 86.1 > 5 85.8 > 6 86.7 > 7 87.9 > 8 89.1 > 9 90 > 10 89 > 11 88 > 12 88 > 13 89.1 > 14 90 > 15 91.2 > 16 89.9 > ... ... > I would like to create a second data frame from the data that looks something like this: > > Event InitialDepth FinalDepth Accumulation InitialTime FinalTime > 1 84.3 90 5.7 1 9 > 2 88 91.2 3.2 11 15 > ... > > I would like to write a program that progresses through the depth column, > point by point, to test if (i+1) - i > x. (where I will set x to exlude the > noise in the data). As long as i+1 is greater than or equal to i, then the > initial depth stays at the first data point and the final value changes to > that in i+n. Once the test is false, this indicates the end of the event, the > accumulation is calculated, all values are saved as event X and a new event isstarted. > I tried using ifelse(), but I do not know how to move through the data and > then save the initial and final values and time stamps in another table. It is probably possible but I would use rle and cumsum # which of the data are increasing ind<-rle(c(T,diff(test$depth)>0)) # what is first depth of increasing interval first<-test$depth[c(1,cumsum(ind$lengths)[!ind$values])] # what is last depth of increasing interval last<-test$depth[cumsum(ind$lengths)[ind$values]] # what is accumulation last-first [1] 1.8 4.2 3.2 -3.8 the similar applies to evaluation which are first and last times of events and/or its duration. Regards Petr > > Thank you very much for your time. > > Kara > > > > > > ______________________________________________ > 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. ______________________________________________ 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.
