Hi all, I have multiple datasets of time series data taken from GPS collars. The collars are supposed to take a fix every hour on the half hour, i.e., 0:30, 1:30, 2:30...23:30, (because it sometimes takes longer for the collars to acquire a location the minute of these locations vary from 30-34) but because of a software glitch in the collars, at random times the collars start taking multiple fixes between programmed fixes, i.e., 22:31, 23:31, 0:31, 1:26, 1:29, 1:30, 1:31, 1:32, 1:33, 1:35, 1:35, 1:35, 1:35, 1:36, 1:36, 1:36, 2:30. These glitches occur approximately once a day throughout the 24 hour and 60 minute cycle. I want to remove all these extra locations from my dataset, but am new to R and haven't figured out a way to do so. I've tried some inelegant solutions involving verbose code, but haven't been able to come up with something that works correctly.
Some things I've tried: #Subsetting out by minute value: >MR1001=read.csv(etc) >datetime<-paste(MR1001$date,MR1001$time) >datetime<-as.POSIXlt(strptime(as.character(datetime), tz="UTC", "%m/%d%Y %H:%M:%S")) >MR1001$min<-datetime$min >t1<-subset(MR1001,min==30|min==31|min==32|min==33|min==34) This works for most of the data, but when the unwanted fixes occur during the 30-34 minute mark of an hour (see example above) they are kept, which I don't want. To deal with this I tried to incorporate the time between fixes in an attempt to write an "ifelse" statement and subset the data that way: >MR1001=read.csv(etc) >MR1001=read.csv(etc) >datetime<-paste(MR1001$date,MR1001$time) >datetime<-as.POSIXlt(strptime(as.character(datetime), tz="UTC", "%m/%d%Y %H:%M:%S")) >MR1001$min<-datetime$min >t1<-subset(MR1001,min==30|min==31|min==32|min==33|min==34) >datetime<-paste(MR1001$date,MR1001$time) >datetime<-as.POSIXct(strptime(as.character(datetime), tz="UTC", "%m/%d%Y %H:%M:%S")) >datetime2<-datetime[-1] >datetime2[length(datetime)]<-datetime2[length(datetime)-1]+3600 >datetime3<-datetime2-datetime >datetime4<-datetime3/60 >datetime5<-as.numeric(datetime4) >t1$diff<-datetime5 This didn't work either though, because when an unwanted fix occurred after a wanted fix the value in the "diff" column was small, and I couldn't figure out how to subset the data in that format (I want to keep the 1st, 2nd, 3rd, and last fix in the example columns below (23:31, 00:31, 01:30, 2:30)): time diff 23:31 60 00:31 58.78 01:30 1.07 01:31 1.07 01:32 1.07 01:33 1.07 01:34 1.08 2:30 60 I hope this explanation is clear and that someone with more experience than me can help with a solution. Thanks very much in advance for your time and help! Nathaniel -- View this message in context: http://r.789695.n4.nabble.com/Need-help-subsetting-time-series-data-tp3254236p3254236.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ 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.
