Ronaldo Reis Junior wrote: > 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) >
Why not just include an error term for Tank in the model? summary(aov(Size~Trt+Error(Tank))) > 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. > ______________________________________________ [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.
