continuous raster to binary
What a fabulous collection of answers!
For my bigger grids that can't reside in memory, I think I need to use calc in regards to Thierry's and Matt's approach, like this:
func <- function(x){x > 3.5} #still need to add "as
r <- calc(r, fun=func, filename = ...)
So, following Rafael's note that reclass was faster than subs alone, here are timings on real data comparing reclass to calc.
func <- function(x){x > ctpt}
system.time(rasCtc <- calc(ras, fun=func, filename=out1, format = "GTiff", datatype = "INT1U"))
user system elapsed 119.16 28.00 147.37
system.time(rasCt <- reclass(ras, rccutpt, filename=out2, format = "GTiff", datatype = "INT1U"))
user system elapsed 119.85 28.38 148.44 They are very close, and perhaps not even significantly different, but calc may be edging out reclass by a small amount. Brilliant! Thanks everyone, for the help. Best, Tim
Matthew Landis <landis at isciences.com> 6/14/2012 11:37 AM >>>
In terms of Tim's example: plot(r) r[] <- as.numeric(r[] > 3.5) plot(r) works for me. Made only a small change from Thierry's elegant example to return numeric instead of boolean. M
On 6/14/2012 9:56 AM, ONKELINX, Thierry wrote:
How about rs<- r> 0.35 or rs<-(r> 0.35) * 1 untested! Best regards, Thierry ir. Thierry Onkelinx Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest team Biometrie& Kwaliteitszorg / team Biometrics& Quality Assurance Kliniekstraat 25 1070 Anderlecht Belgium + 32 2 525 02 51 + 32 54 43 61 85 Thierry.Onkelinx at inbo.be<mailto:Thierry.Onkelinx at inbo.be> www.inbo.be<http://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 Van: r-sig-geo-bounces at r-project.org [mailto:r-sig-geo-bounces at r-project.org] Namens Tim Howard Verzonden: donderdag 14 juni 2012 15:02 Aan: r-sig-geo at r-project.org Onderwerp: [R-sig-Geo] continuous raster to binary All, I'd like to convert a continuous raster to binary (0, 1). Here's what I've come up with library(raster) #build the sample raster r<- raster(ncol=100, nrow=100) r[]<- round(runif(ncell(r)) * 10) #set up a cut point, cut it ctpts<- c(0,3.5,10) rc<- cut(r,breaks=ctpts) #since the result from cut was a raster with values c(1,2), use subs to change to c(0,1) subdf<- data.frame(from=c(1,2), to=c(0,1)) rs<- subs(rc, subdf, subsWithNA=TRUE) rs My questions: 1. Is there a more efficient way? (I'll be doing this to many large rasters) 2. Using 32-bit R, subs bails with a memory error, even if a file is specified (cut runs fine). I can move to 64-bit R on a different machine, but it would be nice to be able to run it on this 32-bit machine. Any suggestions? Thanks in advance, Tim ~
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