loops in rasterEngine

Actually, I have several rasters of more than 440 000 000 pixels (MODIS covering all Canada) and I have a 32-cores machine so I would like to take advantage of it! ;-)

Time is money (really?!!)

Thanks again!
yan

Yan Boulanger, Chercheur scientifique / Research scientist
Ressources Naturelles Canada, Canadian Forest Service
Centre de Foresterie des Laurentides
1055, rue du P.E.P.S.
C.P. 10380, succ. Sainte-Foy
Qu?bec (Qu?bec) Canada
G1V 4C7
Tel. : +1 418 649-6859

From: Forrest Stevens [mailto:forrest at ufl.edu]
Sent: 12 mars 2014 22:25
To: Boulanger, Yan
Cc: r-sig-geo at r-project.org
Subject: Re: [R-sig-Geo] loops in rasterEngine

Hi Yan, I guess I would be surprised for such a simple process if rasterEngine() would be worth the overhead? Though, admittedly, Jonathan Greenberg might have more information on the topic.  To do such an operation this is the approach I would take without using rasterEngine():


for (i in 1:5) {
  assign(paste("Safranyik_zones_1961_1990b_",i, sep=""), Safranyik_zones_1961_1990b == i)
}


To do it using rasterEngine() this is the function definition that I would use. This of course requires that you've already created a cluster using one of the various supported parallel backends otherwise you'll gain nothing from the parallel processing.


require("spatial.tools")

## Begin a parallel cluster and register it with foreach:
## The number of nodes/cores to use in the cluster
cpus = 2
cl <- makeCluster(spec = cpus, type = "PSOCK", methods = FALSE)
## Register the cluster with foreach:
registerDoParallel(cl)

##       Or use the following, quick and dirty way:
#sfQuickInit(cpus=2)

fun_zone <- function( zones, i, ...) {
  return(zones == i)
}

for (j in 1:5){
  assign(paste("Safranyik_zones_1961_1990b_",j, sep=""), rasterEngine( zones=Safranyik_zones_1961_1990b, args=list("i"=j), fun=fun_zone) )
}

stopCluster(cl)
#sfQuickStop()


Hope this helps,
Forrest

--
Forrest R. Stevens
Ph.D. Candidate, QSE3 IGERT Fellow
Department of Geography
Land Use and Environmental Change Institute
University of Florida
www.clas.ufl.edu/users/forrest<http://www.clas.ufl.edu/users/forrest>

On Wed, Mar 12, 2014 at 8:51 PM, Boulanger, Yan <Yan.Boulanger at rncan-nrcan.gc.ca<mailto:Yan.Boulanger at rncan-nrcan.gc.ca>> wrote:
Hi folks,

I guess I have a lot to learn to write functions but I'm stuck when using rasterEngine. It seems that it should be very easy to do but I'm missing something, apparently... I have a raster, Safranyik_zones_1961_1990, with values (integer) from 1 to 5. I would like to create five rasters for which value will be 1 when the raster Safranyik_zones_1961_1990 is equal to "i", and NA otherwise. I would like to run everything in a loop . Here's what I thought would be ok.

fun_zone <- function(Safranyik_zones,i,...) {
Safranyik_zonesb <- Safranyik_zones
Safranyik_zonesb[] <- NA
Safranyik_zonesb[Safranyik_zones == i] <- 1
return(Safranyik_zonesb)
}

for (i in 1:5){
Safranyik_zones_1961_1990b <- rasterEngine(Safranyik_zones=Safranyik_zones_1961_1990,i=i, fun=fun_zone)
assign(paste("Safranyik_zones_1961_1990b_",i, sep=""),Safranyik_zones_1961_1990b[[1]])
}

Of course, it says that ? i ? is missing...:

Erreur dans Safranyik_zones == i : 'i' est manquant

Any help?

Thanks in advance,

Yan


Yan Boulanger, Chercheur scientifique / Research scientist
Ressources Naturelles Canada, Canadian Forest Service
Centre de Foresterie des Laurentides
1055, rue du P.E.P.S.
C.P. 10380, succ. Sainte-Foy
Qu?bec (Qu?bec) Canada
G1V 4C7
Tel. : +1 418 649-6859




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