R help - Aug 2003 - floodfill with matrix data

Dear R users,

I'm trying to do some sort of "floodfill" or "seedfill"
with data stored
within a matrix in R (usually floating numbers), where a marker value is 
given to specify the limits of an area to be filled. A reduced example 
may demonstrate this below. Although I wrote a simple C function for 
this, it would be very helpful to find a more professional solution.

Any suggestions or code snippets are greatly appreciated.

Thomas Petzoldt


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The problem:

## (1) Given the following matrix

z <- matrix(c(0,0,0,0,0,0,
               0,1,1,1,1,0,
               0,1,0,0,1,0,
               0,1,1,1,1,0,
               0,1,0,0,1,0,
               0,1,0,1,1,0,
               0,0,0,0,0,0), nrow=6, ncol=7)
image(z)

## (2) _a_procedure_is_wanted to
# "floodfill" all zeroes with 2 "outside 1"
# to give

## (3) the following result:

z <- matrix(c(2,2,2,2,2,2,
               2,1,1,1,1,2,
               2,1,0,0,1,2,
               2,1,1,1,1,2,
               2,1,2,2,1,2,
               2,1,2,1,1,2,
               2,2,2,2,2,2), nrow=6, ncol=7)

image(z)

Barry Rowlingson wrote:
> Howabout this i just bashed up from a quick search:
> 
>  boundaryFill <- function(mat, x,y,fill,boundary)
[...]
>  note it fills 4-connected regions. I wouldnt like to do it on anything 
> complex since it'll be awful slow....
Yes, this is in principle the same solution I use during aan external C 
function. However, the problem is not only speed, but the large amount 
of stack memory with larger matrices (say 100 x 100) due to recursion, 
no matter if I use options(expression = large_value) or not.

Thank you

Thomas