[R] "Spreading risk" in a matrix

[ONKELINX, Thierry]

Have a look at the buffer function in the adehabitat package. 

HTH,

Thierry

------------------------------------------------------------------------
----
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
Cel biometrie, methodologie en kwaliteitszorg / Section biometrics,
methodology and quality assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium 
tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be 
www.inbo.be 

To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org]
Namens ACroske
Verzonden: vrijdag 18 juli 2008 20:24
Aan: r-help op r-project.org
Onderwerp: [R] "Spreading risk" in a matrix


I have a binary matrix that represents a map of invasive species risk (1
=
infested; 0 = uninfested). It started as a matrix of probabilities
(developed in ArcMap) that I converted to binary with this R code:
binary.matrix<-matrix(rbinom(length(prob.matrix),prob=prob.matrix,size=1
),nrow=nrow(prob.matrix))

Now, I would like to "spread" the risk for year 2 of the invasion. I'd
like
to do this by location, so, for every cell that is currently a 1, next
year
it's immediate neighbors (above, below, to the right and left) would
also
become ones. Here is a function I came up with to attempt this (clearly,
my
function writing is rough, to say the least):

matrix.function<-function(N){
  
binary.matrix<-matrix(rbinom(length(prob.matrix),prob=prob.matrix,size=1
),nrow=nrow(prob.matrix))
   res<-numeric(N)
       for (i in 1:N){
       res[i]<-binary.matrix
            if (res[i]==1){
            res[,i+1]=1
            res[,i-1]=1
            }
       }
}

When I run this code, I get many messages saying "In
res[i]<-binary.matrix :
number of items to replace is not a multiple of replacement length"

I know that if I actually got this to work, it would be a string of
numbers
(because of the "numeric"), but I'm just working with my limited
function-writing knowledge, and I assumed it would be possible to
convert
the results to a matrix later on.

I'm aware that this function is probably a disaster, but that's why I'm
here!
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