I have some code that loops over a list of study IDs (ids) and turns them into separate polygons/spatial points. On the first execution of the loop it produces the following error:
Error in (function (x) : attempt to apply non-function
This is from the raster::rasterToPoints function. I've looked at the examples in the help section for this function and passing fun=NULL seems to be an acceptable method (filters out all NA values). All the values are equal to 1 anyways so I tried passing a simple function like it suggests such as function(x){x==1}. When this didn't work, I also tried to just suppress the error message but without any luck using try() or tryCatch().
Main questions:
1. Why does this produce an error at all?
2. Why does it only display the error on the first run through the loop?
Reproducible example:
library(ggplot2)
library(raster)
library(sf)
library(dplyr)
pacific <- map_data("world2")
pac_mod <- pacific
coordinates(pac_mod) <- ~long+lat
proj4string(pac_mod) <- CRS("+init=epsg:4326")
pac_mod2 <- spTransform(pac_mod, CRS("+init=epsg:4326"))
pac_rast <- raster(pac_mod2, resolution=0.5)
values(pac_rast) <- 1
all_diet_density_samples <- data.frame(
lat_min = c(35, 35),
lat_max = c(65, 65),
lon_min = c(140, 180),
lon_max = c(180, 235),
sample_replicates = c(38, 278),
id= c(1,2)
)
ids <- all_diet_density_samples$id
for (idnum in ids){
poly1 = all_diet_density_samples[idnum,]
pol = st_sfc(st_polygon(list(cbind(c(poly1$lon_min, poly1$lon_min, poly1$lon_max, poly1$lon_max, poly1$lon_min), c(poly1$lat_min, poly1$lat_max, poly1$lat_max, poly1$lat_min, poly1$lat_min)))))
pol_sf = st_as_sf(pol)
x <- rasterize(pol_sf, pac_rast)
df1 <- raster::rasterToPoints(x, fun=NULL, spatial=FALSE) #ERROR HERE
df2 <- as.data.frame(df1)
density_poly <- all_diet_density_samples %>% filter(id == idnum) %>% pull(sample_replicates)
df2$density <- density_poly
write.csv(df2, paste0("pol_", idnum, ".csv"))
}
Any help would be greatly appreciated!
These are error messages, but not errors in the strict sense as the script continues to run, and the results are not affected. They are related to garbage collection (removal from memory of objects that are no longer in use) and this makes it tricky to pinpoint what causes it (below you can see a slightly modified example that suggests another culprit), and why it does not always happen at the same spot.
Edit (Oct 2022)
These annoying messages
Error in x$.self$finalize() : attempt to apply non-function
Error in (function (x) : attempt to apply non-function
Will disappear with the next release of Rcpp, which is planned for Jan 2023. You can also install the development version of Rcpp like this:
install.packages("Rcpp", repos="https://rcppcore.github.io/drat")