[R-sig-Geo] raster: extract() based in a pixel value

[Rafael Wüest]

Hi there

adapt your function for extraction as follows:

percentual_1s<- function(x,...) {
  leng1<-length(which(x==1))
  lengtotal<-length(x) 
  perc<-(leng1/lengtotal)*100
  return(perc)
}

And add "na.rm = FALSE" in the extract call:

cent_max <- extract(ras, pts[,1:2], buffer = 1000000, fun=percentual_1s, df=TRUE, na.rm = FALSE)

That gives me:

head(cent_max)
  ID    layer
1  1 49.81865
2  2 50.27545
3  3 50.03113
4  4 50.29819
5  5 50.39391
6  6 48.89556

The values I get make sense to me (around 50%).

HTH, Rafi


> On 22 Sep 2020, at 14:26, ASANTOS via R-sig-Geo <r-sig-geo using r-project.org> wrote:
> 
> Dear R-sig-geo Members,
> 
> I'd like to use de extract() function using the raster package for 
> calculate a proportion of pixel with "1"s values inside a buffer given 
> some coordinates in a raster. I try to create a function for this 
> without success, in my hypothetical example:
> 
> #Package
> library(raster)
> 
> # Create a raster
> ras <- raster(ncol=1000, nrow=1000)
> set.seed(0)
> values(ras) <- runif(ncell(ras))
> values(ras)[values(ras) > 0.5] = 1
> values(ras)[values(ras) < 0.5] = NA
> 
> # Create some coordinates
> pts<-sampleRandom(ras, size=30, xy=TRUE)
> pts.df<-as.data.frame(pts)
> pts.df$area<-rnorm(30, mean=10)## Here just for create a artificial 
> covariate without any direct implication in my question
> 
> #Function for extract proportion of 1s values
> percentual_1s<- function(x,...) {
> � leng1<-length(values(x) ==1) # length of 1s pixels values
> � lengtotal<-length(x) # total length of pixels inside buffer
> � perc<-(leng1/lengtotal)*100
> � return(perc)
> }
> 
> # Extract the desirable proportion in a circular 100000 units buffer
> cent_max <- extract(ras, # raster layer
> ��� cbind(pts.df$x,pts.df$y),��� # SPDF with centroids for buffer
> ��� buffer = 100000,������������ # buffer size
> ��� fun=percentual_1s,���������� # what to value to extract
> ��� df=TRUE)
> 
> 
> Here doesn't work, despite the code look like Ok. My perfect output is:
> 
> #������� x����� y layer����� area�� percentual_1s
> #1 -109.26 -43.65���� 1 10.349010�� 23.15
> #2�� 93.42 -87.21���� 1� 9.861920�� 45.18
> #3�� 57.06� 86.85���� 1� 8.642071�� 74.32
> #4 -109.98 -45.63���� 1 10.376485�� 11.56
> #5� -92.34� 37.89���� 1 10.375138�� 56.89
> #6�� 19.62� 21.51���� 1� 8.963949�� 88.15
> 
> 
> Please any ideas or any another package that help in this operation?
> 
> Thanks in advanced,
> 
> 
> -- 
> Alexandre dos Santos
> Geotechnologies and Spatial Statistics applied to Forest Entomology
> Instituto Federal de Mato Grosso (IFMT) - Campus Caceres
> Caixa Postal 244 (PO Box)
> Avenida dos Ramires, s/n - Vila Real
> Caceres - MT - CEP 78201-380 (ZIP code)
> Phone: (+55) 65 99686-6970 / (+55) 65 3221-2674
> Lattes CV: http://lattes.cnpq.br/1360403201088680
> OrcID: orcid.org/0000-0001-8232-6722
> ResearchGate: www.researchgate.net/profile/Alexandre_Santos10
> Publons: https://publons.com/researcher/3085587/alexandre-dos-santos/
> --
> 
> 
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