[R] vectorizing a matrix computation

[Wolski]

Hallo Christoph!

Using apply and sweep.
Both of them accept  as the second argument (MARGIN) a vector which specifies the dimension.

?apply
?sweep.

To specify the subscripts accurately I always need some trials, and to run tests, so I cant you provide with the final solution.

Hope it helps anyway.

Sincerely Eryk.



*********** REPLY SEPARATOR  ***********

On 7/20/2004 at 11:31 AM Christoph Lehmann wrote:

>>>Dear R users
>>>
>>>I have a 4-dimensional matrix (actually several 3d (x,y, slices) 
>>>matrices appended over time (volumes))
>>>
>>>say, e.g. I want to z-transform the data (subtract the mean and divide 
>>>by the std-deviation)
>>>
>>>for (slice in 1:slices) {
>>>     for (x in 1:x.dim) {
>>>         for (y in 1:y.dim) {
>>>         t <- as.matrix(my.matrix[x,y,slice,1:volumes])
>>>         for (vol in 1:volumes) {
>>>             my.matrix.transformed[x,y,slice,vol] <- 
>>>(my.matrix[x,y,slice,vol] - mean(t))/sqrt(var(t))
>>>             }
>>>         }
>>>     }
>>>}
>>>
>>>how can I vectorize such a function using, one of the *apply functions?
>>>
>>>many thanks
>>>
>>>Cheers
>>>
>>>Christoph
>>>
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>>>R-help at stat.math.ethz.ch mailing list
>>>https://www.stat.math.ethz.ch/mailman/listinfo/r-help
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Dipl. bio-chem. Eryk Witold Wolski    @    MPI-Moleculare Genetic   
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