[R-sig-Geo] Fwd: ifelse with multiple rasters

[Jonathan Greenberg]

Laura:

If this is a straight masking procedure, you can do some
multiplication tricks in raster like:

output = rst_a*rst_B*2

or look at
?overlay

or take a look at
?mask

I suspect mask and overlay are faster than the raster algebra
statement (Robert, is this correct?)

If you want to use rasterEngine for parallel processing, you can do
something like this:

library(spatial.tools)

# Set X to the number of CPUs you want top use and uncomment this for
parallel processing:
# sfQuickInit(cpus=X)

rst_test <- function(rst_a,rst_B)
{
return(ifelse(rst_a==0 & rst_B==1,2,0))
}

# Fill in the rasters you intend to use here:
raster_check <-
rasterEngine(rst_a=someraster,rst_B=someotherraster,fun=rst_test)

# Uncomment to stop the parallel engine if need be:
# sfQuickStop()

--j

On Mon, Feb 24, 2014 at 8:16 AM, Laura Poggio <laura.poggio at gmail.com> wrote:
> Dear list,
> I am struggling to find a way to do a simple if statement with multiple
> rasters in raster.
>
> For example:
> ifelse(rst_a==0 & rst_B=1,2,0)
>
> Which is the simplest and most efficient way to implement it? especially
> when considering large (>10,000,000 cells) rasters?
>
> Thank you in advance
>
> Laura
>
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>
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-- 
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
259 Computing Applications Building, MC-150
605 East Springfield Avenue
Champaign, IL  61820-6371
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
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