MAtrix addressing

From: David Winsemius <dwinsemius at comcast.net>
Date: January 26, 2011 8:32:30 AM EST
To: Alaios <alaios at yahoo.com>
Subject: Re: [R] MAtrix addressing


On Jan 26, 2011, at 7:58 AM, Alaios wrote:

Unfortunately right now is convoluted... by I was trying to find  
some solution.
Bring again this picture in front of u
http://img545.imageshack.us/i/maptoregion.jpg/

Consider f a function that gets as input the coords
so
f(-1,-1) should return the value of the bottom left point
f(1,1) should return the value of the top right point.


A.For me an area is approximated by a matrix so each cell of the  
matrix corresponds to a fixed value in a small sub-area.
So When my function gets coords like f(0,0.3) should find the  
corresponding sub-area.

B. This is want to do
I also have a data structure called matrix that in every cell has  
the appropriate values of that area.

A+B => Combine these two and have a function that returns the  
appropriate value of a subarea given its coords. Attention my area  
spans from -1 to 1 in y plane and from -1 to 1 in the x plane.

Was it clearer this way? (Why is always so hard to me to explain  
even simple tasks?)

Regards
Alex

--- On Wed, 1/26/11, David Winsemius <dwinsemius at comcast.net> wrote:

From: David Winsemius <dwinsemius at comcast.net>
Subject: Re: [R] MAtrix addressing
To: "Alaios" <alaios at yahoo.com>
Cc: R-help at r-project.org
Date: Wednesday, January 26, 2011, 12:49 PM

On Jan 26, 2011, at 2:47 AM, Alaios wrote:

The reason is the following image
http://img545.imageshack.us/i/maptoregion.jpg/
In the picture above you will find the indexes for

each cell.

Also you will see that I place that matrix inside a

x,y region that spans from -1 to 1. I am trying to write one
function that will get as argument a (x,y) value x e[-1,1] y
e[-1,1] and will return the indexes of that cell tha x,y
value correspond to.

I really do not have a clue how I should try to

approach that to solve it. So based on some version I had
for 1-d vector I tried to extend it for 2-d. I used
findInterval as a core to get results.

Unfortunately my code fails to produce accurate

results as my approach 'assumes' (this is something
inhereted by the find Interval function) that the numbering
starts bottom left and goes high top right.

You will find my code below

If one wants to take an ordinary r matrix and reorder it in
the manner you describe:

mtx2 <- mtx[ nrow(mtx):1, ]

Whether that is an efficient way to get at the sokution
your you programming task I cannot say. It sounds as though
it has gotten too convoluted. I was not able to comprehend
the overall goal from your problem description.

sr.map <- function(sr){
# This function converts the s(x,y) matrix into a

function x that spans #from -1 to 1 and y spans from -1 to
1.

# Input: sr a x,y matrix containing the shadowing

values of a Region

    breaksX <- seq(from=-1, to

= 1, length = nrow(sr) +1L )

    breaksY <- seq(from=-1, to

= 1, length = ncol(sr) + 1L)

    function(x,y){ # SPAGGETI CODE

FOR EVER

        indx <-

findInterval(x, breaksX,rightmost.closed=TRUE)

    indy <-

findInterval(y, breaksY,rightmost.closed=TRUE)

    c(indx,indy)
    }
}

sr<-matrix(data=seq(from=1,to=36),nrow=6,ncol=6,byrow=TRUE)

f.sr.map<-sr.map((sr))
f.sr.map(-0.1,-0.1)
f.sr.map(0.1,0.1)



Best Regards
Alex





--- On Wed, 1/26/11, David Winsemius <dwinsemius at comcast.net>

wrote:

From: David Winsemius <dwinsemius at comcast.net>
Subject: Re: [R] MAtrix addressing
To: "Alaios" <alaios at yahoo.com>
Cc: R-help at r-project.org
Date: Wednesday, January 26, 2011, 2:54 AM

On Jan 25, 2011, at 4:50 PM, Alaios wrote:

Hello
I would like to ask you if it is possible In R

Cran to

change the default way of addressing a matrix.

for example
matrix(data=seq(from=1,to=4,nrow=2,ncol=2, by

row

numbering) # not having R at this pc

will create something like the following
1 2
3 4

the way R address this matrix is from top left

corner

moving to bottom right.

The cell numbers in that way are
1 2
3 4

IS it possible to change this default

addresing number

to something that goes bottom left to top right?

In this

simple case I want to have

3 4
1 2

Would that be possible?

Yes. it's possible but ... why?

I would like to thank y for your help
Regards
Alex

David Winsemius, MD
West Hartford, CT