[R] multidimensional lists

From: Evan Cooch <cooch17_at_verizon.net>
Date: Wed 27 Sep 2006 - 16:07:48 GMT


In the process of moving a number of my scripts from MATLAB -> R, I've discovered that there is no 'pure' equivalent of MATLAB's cell arrays, which I use quite often. Basically, I create matrices (as a cell array) where each element of the matrix is itself a matrix (e.g., 2x2 cell array where each element of the array is another matrix). I pass these cell arrays to various functions which then do clever things with the various matrices (of course) - basically, I need to be able to pass collections of matrices to functions to do various things, and I need to be able to control the dimensionality of the cell array to preserve some structural relationships among the matrices in the array. The cell array in MATLAB handles this with aplomb.

So far, in R, I've used lists. Given (say) 4 matrices (A,B,C,D), in MATLAB I can use

test={A,B,C,D} for a row vector cell array, or

test={A;B;C;D} for a column vector cell array.

In R, I get more or less the same thing using

test=list(A,B,C,D)

but this only gives me a row list. For a bunch of technical reasons, I need to be able to control the orientation (as noted)- this is especially true for n-dimensional cell arrays. In MATLAB, for example, I could generate a (say) 2x2 cell array using

test={A B;C D}

The only way I can figure out how to do this in R is using something like

test=list(A,B,C,D);
dim(test) < c(2,2);

This seems to work, but defaults to bycolumn (in other words, instead of

A B
C D

I get

A C
B D

)

So, I follow with

test=t(test) as needed to flip the thing around to byrow.

OK, so the question is - is there a better way? This *seems* to work, but I'm discovering that R is a lot like working with LaTeX (something I know much more about) - you can do most things, but there is often a more elegant way if you can figure out how to find out about it.

Thanks in advance...



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