On Sep 17, 2012, at 4:15 PM, Julie Lee-Yaw wrote: > Hi > > I have a dataframe similar to: > >> Sample<-c(1,1,1,2,2,2,3,3,3) > >> Time<-c(1,2,3,1,2,3,1,2,3) > >> Mass<-c(3,3.1,3.4,4,4.3,4.4,3,3.2,3.5) > >> mydata<-as.data.frame(cbind(Sample,Time,Mass)) > Please tell me where you learned that as.data.frame(cbind(.)) construction.
> ( > Sample Time Mass > 1 1 1 3.0 > 2 1 2 3.1 > 3 1 3 3.4 > 4 2 1 4.0 > 5 2 2 4.3 > 6 2 3 4.4 > 7 3 1 3.0 > 8 3 2 3.2 > 9 3 3 3.5 > > where for each sample, I've measured mass at different points in time. > > I now want to calculate the difference between Mass at Time 2 and 3 for each > unique Sample and store this as a new variable called "Gain2-3". So in my > example three values of 0.3,0.1,0.3 would be calculated for my three unique > samples and these values would be repeated in the table according to Sample. > I am thus expecting: > >> mydata #after adding new variable mydata$gain2.3 <- with( mydata, ave( Mass , Time, FUN=function(x) diff(x[2],x[3]) ) ) > > Sample Time MassGain2-3 > 1 1 1 3.00.3 > 2 1 2 3.1 0.3 > 3 1 3 3.4 0.3 > 4 2 1 4.0 0.1 > 5 2 2 4.3 0.1 > 6 2 3 4.4 0.1 > 7 3 1 3.0 0.3 > 8 3 2 3.2 0.3 > 9 3 3 3.5 0.3 > > mydata$gain2.3 <- with( mydata, ave( Mass , Sample, FUN=function(x) > (x[3]-x[2]) ) ) > mydata Sample Time Mass gain2.3 1 1 1 3.0 0.3 2 1 2 3.1 0.3 3 1 3 3.4 0.3 4 2 1 4.0 0.1 5 2 2 4.3 0.1 6 2 3 4.4 0.1 7 3 1 3.0 0.3 8 3 2 3.2 0.3 9 3 3 3.5 0.3 > Does anyone have any suggestions as to how to do this? I've looked at the > various apply functions but I can't seem to make anything work. I'm fairly > new to R and would appreciate specific suggestions. -- David Winsemius, MD Alameda, CA, USA ______________________________________________ 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.
