Em Quinta 21 Junho 2007 16:56, Thomas Miller escreveu: > I am transitioning from SAS to R and am struggling with a relatively simple > analysis. Have tried Venables and Ripley and other guides but can't find a > solution. > > I have an experiment with 12 tanks. Each tank holds 10 fish. The 12 tanks > have randomly assigned one of 4 food treatments - S(tarve), L(ow), M(edium) > and H(igh). There are 3 reps of each treatment. I collect data on size of > each fish at the end of the experiment. So my data looks like > > Tank Trt Fish Size > 1 S 1 3.4 > 1 S 2 3.6 > .... > 1 S 10 3.5 > 2 L 1 3.4 > .... > 12 M 10 2.1 > > To do the correct test of hypothesis using anova, I need to calculate the > tank means and use those in the anova. I have tried using tapply() and > by() functions, but when I do so I "loose" the treatment level because it > is categorical. I have used > Meandat<tapply(Size,list(Tank, Trt), mean) > > But that doesn't give me a dataframe that I can then use to do the actual > aov analysis. So what is the most efficient way to accomplish the analysis > > Thanks > > Tom Miller
Tom, try the aggregate funtion. Somethink like this meandat <- aggregate(Size,list(Tank,Trt),mean) Inte Ronaldo -- > Prof. Ronaldo Reis Júnior | .''`. UNIMONTES/Depto. Biologia Geral/Lab. de Ecologia | : :' : Campus Universitário Prof. Darcy Ribeiro, Vila Mauricéia | `. `'` CP: 126, CEP: 39401-089, Montes Claros - MG - Brasil | `- Fone: (38) 3229-8187 | [EMAIL PROTECTED] | [EMAIL PROTECTED] | http://www.ppgcb.unimontes.br/ | ICQ#: 5692561 | LinuxUser#: 205366 ______________________________________________ [email protected] 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.
