R help - Nov 2007 - Resample a matrix (table)

I have a matrix of values... for exemple the matrix could be 100 rows
and 50 columns...
I would like to resample the matrix to obtain a new matrix -> a 10x5 matrix
So i need to calculate a new value for every cell, i would like to use a
weightened mean to do this. I explain this thing better:
In the exemple the original matrix would be divided into 50
partial-matrix, for every partial-matrix should be extracted a value
obtained from a weightened mean: the cell at center of the
partial-matrix should have the max importance into the mean, the fhurter
cell should have the lower importance (something like a gaussian shape,
where i can decide the sigma used).... In this way i'll obtain a
resampled matrix with the values calculated using a weightened mean of
the single partial-matrix...

Is there anybody who can suggest me a way to do this??? is there a
function that can do this?

PS: sorry for my english... and... im a newbie, please try to explain in
a simple way.. thank you

Luca Penasa,
geology student,
University of Padua, Italy


 
 
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Hi Luca,

One (not very elegant) way of doing this is to use
double loop as below:
Let A be your matrix (100x50), W your weights matrix
(10x10) and you want to produce matrix B (10X5)
You can do:

B <- matrix(0,nrow=10,ncol=5)
for (i in 1:10) for (j in 1:5) B[i,j] <-
sum(W*A[(10*(i-1)+1):10*i,(10*(j-1)+1):10*j])

Regards,

Moshe.


--- Luca Penasa <luca.penasa at email.it> wrote:
> I have a matrix of values... for exemple the matrix
> could be 100 rows
> and 50 columns...
> I would like to resample the matrix to obtain a new
> matrix -> a 10x5 matrix
> So i need to calculate a new value for every cell, i
> would like to use a
> weightened mean to do this. I explain this thing
> better:
> In the exemple the original matrix would be divided
> into 50
> partial-matrix, for every partial-matrix should be
> extracted a value
> obtained from a weightened mean: the cell at center
> of the
> partial-matrix should have the max importance into
> the mean, the fhurter
> cell should have the lower importance (something
> like a gaussian shape,
> where i can decide the sigma used).... In this way
> i'll obtain a
> resampled matrix with the values calculated using a
> weightened mean of
> the single partial-matrix...
> 
> Is there anybody who can suggest me a way to do
> this??? is there a
> function that can do this?
> 
> PS: sorry for my english... and... im a newbie,
> please try to explain in
> a simple way.. thank you
> 
> Luca Penasa,
> geology student,
> University of Padua, Italy
> 
> 
>  
>  
>  --
>  Email.it, the professional e-mail, gratis per te:
> http://www.email.it/f
>  
>  Sponsor:
>  In REGALO 'All the Good Thing' di NELLY FURTADO
>  Clicca qui:
>
http://adv.email.it/cgi-bin/foclick.cgi?mid=6617&d=12-11
> 
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