How to manipulate an abitrary dimensioned array.

-----Original Message-----
From: Mike Meyer [mailto:mikem at salter-point.com] 
Sent: Thursday, October 27, 2005 3:43 PM
To: Berton Gunter
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] How to manipulate an abitrary dimensioned array.

Thanks for the suggestion.
Perhaps I can see how to use apply to get the ratio, but say 
I also want 
to return X[,,,,1] in a general way.  Maybe I am being dense 
but I just 
don't see it --- probably as a result of too much Perl/Python/Java 
recently that is clouding my mind.

So can someone suggest a general function that will give me the last 
layer of an arbitrary dimensioned array?

Berton Gunter wrote:

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