[R] Analog to matlab repmat function

[Prof Brian Ripley]

On Mon, 29 May 2006, Daniil Ivanov wrote:

> Oops, mistake, should be
>
> data = data - repmat(mean(data,1),[130 1 1 1]);
>
> Sorry.

I am afraid I do not know what that actually does in matlab, except that 
it looks like subtracting (not extracting) a mean.

Functions which I would expect you to be using are sweep(), rowMeans or 
colMeans().  Something like

arr <- sweep(arr, 2:4, colMeans(arr, 1))

perhaps?  (Using 'data', the name of a system R object, is a good way to 
sidetrack your audience and so best avoided.)


> On 5/29/06, Daniil Ivanov <daniil.ivanov at gmail.com> wrote:
>> Hello,
>>
>>  I'm trying to switch from Matlab to R-project, and having some difficulties.
>>  I make a use of multidimensional matrices. For example, I need to extract
>>  mean from one of the dimensions:
>>
>>  % we have matrix data of size: 130 x 11 x 350 x 2
>>  data = data - repmat(mean(data,3),[130 1 1 1]);
>>
>>  In R project I managed to do that in a very pervarsive way:
>>
>>  # mean(data,3) in R
>>  base <- apply(data,c(2,3,4),mean)

Probably rowMeans(data, 1) is meant.

>>  # repmat(...,[130 1 1 1])
>>  base <- rep(base,130)
>>  dim(base) <- c(11,2,350,130)
>>  base <- aperm(base,c(4,1,2,3))
>>  # data = data - repmat
>>  data <- data - base;
>>
>>  Could you please show me a more elegant way of doing the same in R :)
>>
>> Thanks, Daniil.
>>
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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