Re: [R] anova on data means

From: Ronaldo Reis Junior <chrysopa_at_gmail.com>
Date: Thu, 21 Jun 2007 17:22:33 -0300

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 | ronaldo.reis_at_unimontes.br | chrysopa_at_gmail.com | http://www.ppgcb.unimontes.br/ | ICQ#: 5692561 | LinuxUser#: 205366 ______________________________________________ R-help_at_stat.math.ethz.ch 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.
Received on Thu 21 Jun 2007 - 20:28:57 GMT

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