[R] spinning and flipping arrays

Spencer Graves spencer.graves at pdf.com
Mon May 26 22:19:27 CEST 2003

You may also be interested in "aperm", which permutes the indices of an 
array.  Thus, t(x) is the same as aperm(x, 2:1).

spencer graves

Bill Rising wrote:
> On 5/26/2003 15:05, Spencer Graves wrote
>>	  I know of no single function to do this;  perhaps someone else does. 
>> I don't have time to write and debug functions to do this myself, but 
>>it should be easy enough to write functions like the following:
>>flip3 <-
>>  n3 <- dim(x)[3]
>>  x[,,n3:1]
>>spin3 <-
>>function(x, k=1){
>>  n3 <- dim(x)[3]
>>  x[,,1+(((1+k):(n3+k))%%n3)]
> These are pretty much what I'd figured out...
>>With a little more work, I could generate functions that would do this 
>>for any dimension of arrays with any number of dimensions.  To do that, 
>>I might have to compute S-Plus commands using "cmd <- paste(...)" and 
>>then execute them using "eval(parse(text=cmd))".
> This last piece is what I think I needed. I had been trying to just put 
> the 
> /argument/ to the "[" command together, instead of putting together the 
> entire command.
> Thanks for the tip. I'll keep working on it.
> Bill
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