[R] vector-factor operation

[Murray Jorgensen]

Thanks to Berwin Turlach and Petr Pikal for

tapply(vec, Fac, mean)[Fac]

and Gabor Grothendieck Thomas Lumley for

ave(vec,Fac)  .

Looking at the code for tapply and ave I guess that the latter is to be 
preferred.

Murray Jorgensen

Gabor Grothendieck wrote:
> Look at ?ave
> 
> ave(vec, Fac)
> ave(vec, Fac, FUN = mean) # same
> ave(vec, Fac, FUN = sd)
> 
> On 4/14/06, Murray Jorgensen <maj at stats.waikato.ac.nz> wrote:
>> I found myself wanting to average a vector [vec] within each level of a
>> factor [Fac], returning a vector of the same length as vec. After a
>> while I realised that
>>
>> lm1 <- lm(vec ~ Fac)
>> fitted(lm1)
>>
>> did what I want.
>>
>> But there must be another way to do this, and it would be good to be
>> able to apply other functions than mean() in this way.
>>
>> Cheers, Murray

-- 
Dr Murray Jorgensen      http://www.stats.waikato.ac.nz/Staff/maj.html
Department of Statistics, University of Waikato, Hamilton, New Zealand
Email: maj at waikato.ac.nz                                Fax 7 838 4155
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