[R] vector-factor operation

Murray Jorgensen maj at stats.waikato.ac.nz
Fri Apr 14 07:46:12 CEST 2006

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)

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
Phone  +64 7 838 4773 wk    Home +64 7 825 0441    Mobile 021 1395 862

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