[R] Warning: as.numeric reorders factor data

[Peter Dalgaard BSA]

Bud Gibson <fpgibson at umich.edu> writes:

>  > test <- as.factor(as.character(c(1,2,3,4,5,6,7,8,9,10,11)))
>  > test
>   [1] 1  2  3  4  5  6  7  8  9  10 11
> Levels: 1 10 11 2 3 4 5 6 7 8 9
>  > as.numeric(test)
>   [1]  1  4  5  6  7  8  9 10 11  2  3
> 
> It strikes me that as.numeric should *never* reorder the vector it is
> working on.  There is this workaround for the problem:

as.numeric is not reordering anything. "2" is the 4th level of the
test factor, which in turn is due to alphabetic ordering of the
factor levels in as.factor() [or factor() for that matter]. If you
want to avoid that, set factor levels explicitly:

test <- factor(as.character(c(1:11)),levels=c(1:11))
test
as.numeric(test)

I suppose that similar treatment of your "trial" variable prior to 
calling aggregate() could solve your problem.

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907