[R] Multi-dimensional function.
Wolfgang Huber
huber at ebi.ac.uk
Fri Jan 4 23:59:38 CET 2008
José Luis Aznarte M. ha scritto:
> Hi there! Happy new year to everyone!
> There's a piece of code that I must write that's driving me crazy.
> Maybe any of you has previous experiences in something similar. Any help
> will be greatly appreciated!
>
> The problem is as follows. I have a matrix Z with dimensions c(m,
> p). I have two vectors
> Gamma and Th with length p.
> What I want to do is, for j in 1:p, for each pair (Gamma[j], Th[j]),
> apply the logistic function to each column of z, using plogis(Z[,j],
> Th[j], 1/Gamma[j]). Then, by concatenating the result of each iteration
> I would obtain a matrix lZ with dimensions c(m, p).
>
> Now, the question is: is there a neat way to do this in a single
> step, i.e., without the obvious loop? I have a not-so-good relationship
> with the "apply" family, but I suspect there should be a way. Sorry if
> this is a silly question...
> Thanks and best wishes for the new year to you all! Salud!
>
Dear Jose,
I think something similar to
lZ = lapply(seq_len(ncol(Z)), function(i) Z[,i])
mapply(plogis, lZ, Th, 1/Gamma)
should do the trick. But I doubt it will lead to better performance, my
understanding is that the for-loop would be more efficient in terms of
CPU-load and memory.
Best wishes
Wolfgang
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