R help - Oct 2005 - How to manipulate an abitrary dimensioned array.

If I have an n1 x n1 x 2 array X I can calculate, say,
X[,,1]/X[,,2].

If it is a 4 dimensional array then I want to be able to calculate
X[,,,1]/X[,,,2], and similarly for higher dimensions.

How can I write a function to do this in a general way without having to 
do a switch for each possible length(dim(X)).  So I want a function g 
that will take an arbitrary dimensioned array, X, and return 
X[,,,1]/X[,,,2], etc.   I know how to do this by turning X into a 
vector, then doing the division, then re-shaping as an array, but that 
doesn't seem very elegant.

What I think I am missing is how to paste/substitute/eval a bunch of 
commas into an array selection.

Thanks, --Mike

--
Mike Meyer,  Seattle WA

Why doesn't apply() already do what you want?

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 
> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Mike Meyer
> Sent: Thursday, October 27, 2005 2:50 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] How to manipulate an abitrary dimensioned array.
> 
> If I have an n1 x n1 x 2 array X I can calculate, say,
> X[,,1]/X[,,2].
> 
> If it is a 4 dimensional array then I want to be able to calculate
> X[,,,1]/X[,,,2], and similarly for higher dimensions.
> 
> How can I write a function to do this in a general way 
> without having to 
> do a switch for each possible length(dim(X)).  So I want a function g 
> that will take an arbitrary dimensioned array, X, and return 
> X[,,,1]/X[,,,2], etc.   I know how to do this by turning X into a 
> vector, then doing the division, then re-shaping as an array, 
> but that 
> doesn't seem very elegant.
> 
> What I think I am missing is how to paste/substitute/eval a bunch of 
> commas into an array selection.
> 
> Thanks, --Mike
> 
> --
> Mike Meyer,  Seattle WA
> 
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