RE: [R] array addition doesn't recycle!
At 01:39 pm -0500 31/03/04, Raubertas, Richard wrote:
Another alternative is to use the underappreciated function
'sweep()':
sweep(A, 1:2, a, +)
I find the following helpful (it's not due to me but I cannot find
the original poster):
%.+% - function(a,x){sweep(a , 2:1 , x ,+ )}
%+.% - function(a,x){sweep(a , 1:2 , x ,+ )}
A - matrix(1:16,4,4)
x - 10^(0:3)
A %+.% x
[,1] [,2] [,3] [,4]
[1,]26 10 14
[2,] 12 16 20 24
[3,] 103 107 111 115
[4,] 1004 1008 1012 1016
A %.+% x
[,1] [,2] [,3] [,4]
[1,]2 15 109 1013
[2,]3 16 110 1014
[3,]4 17 111 1015
[4,]5 18 112 1016
For 3d arrays this generalizes to
%+..% - function(a,x){sweep(a , 1 , x ,+ )}
%.+.% - function(a,x){sweep(a , 2 , x ,+ )}
%..+% - function(a,x){sweep(a , 3 , x ,+ )}
Then if A - array(1:8,rep(2,3)) and x - c(10,100)
A %+..% x et seq give you a consistent method for addition.
--
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
SO14 3ZH
tel +44(0)23-8059-7743
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RE: [R] array addition doesn't recycle!
Another alternative is to use the underappreciated function 'sweep()': sweep(A, 1:2, a, +) Internally this is about the same as your 'A + array(a, c(2,2,2))'. But it has the advantage that it makes explicit what the relationship between the dimensions of 'A' and 'a' is. I find that relying on implicit recycling tends to produce errors that are hard to trace, and code that is hard to understand six months later. Rich Raubertas Merck Co. -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Prof Brian Ripley Sent: Wednesday, March 31, 2004 10:00 AM To: Tamas Papp Cc: R-help mailing list Subject: Re: [R] array addition doesn't recycle! The recycling rules are documented and this is not amongst them. Computer packages do have a tendency to follow their rules rather than read your mind. I suspect A + as.vector(a) is what you intended. On Wed, 31 Mar 2004, Tamas Papp wrote: Hi, I have noticed the following: a - array(1:4, c(2, 2)) A - array(1:4, c(2,2,2)) A + a Error in A + a : non-conformable arrays It works with a matrix + a vector, why doesn't it work with arrays? Am I missing something? How would you do the above operation efficiently (ie I need to add a matrix to each plane of 3-dim array)? At the moment I am using something like A + array(a, c(2,2,2)) but it doesn't seem that efficient. Why do you think is `not that efficient'? Does you have a need to save microseconds? -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UKFax: +44 1865 272595 __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html __ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
