Question

I have experiencing a weird problem with the ‘plot’ function of the ‘raster’ package.

library(raster)
ras <- raster(ncol=10, nrow=10)

EDIT

values(ras) <- runif(ncell(ras))

END EDIT

plot(ras)

Erreur dans as.double(y) : 
cannot coerce type 'S4' to vector of type 'double'

For what I have read on the net, this error depends on the user, and probably depends on the loaded packages. In my case, the problem comes from the fact that r uses the standard ‘plot’ method from the ‘graphics’ package, when it should use the specific ‘raster’ method since ‘ras’ is a rasterLayer object. However, for a reason I do not understand, ‘plot’ is not imported in the ‘raster’ namespace, while all the other functions are.

> raster::plot
Erreur : 'plot' n'est pas un objet exporté depuis 'namespace:raster'

To be compared with :

raster::persp
standardGeneric for "persp" defined from package "graphics"
function (x, ...) 
standardGeneric("persp")
<environment: 0x0cd9eb80>
Methods may be defined for arguments: x
Use  showMethods("persp")  for currently available ones.

Since I do not completely understand how namespaces behave, I am looking for your help ! Is this kind of situation familiar for you, and do you have a way to solve it ? In the meantime, do you know a function to display the content of a namespace (so I could check the content of the raster namespace step by step) ?

PS: I am using R 2.15.2 with RStudio, many packages loaded but all are up to date.

sessionInfo()
R version 2.15.0 (2012-03-30)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=French_Belgium.1252  LC_CTYPE=French_Belgium.1252          LC_MONETARY=French_Belgium.1252 LC_NUMERIC=C                   
[5] LC_TIME=French_Belgium.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] raster_2.0-41 sp_1.0-5     

loaded via a namespace (and not attached):
 [1] grid_2.15.0      hexbin_1.26.0    intervals_0.13.3 lattice_0.20-6   rgdal_0.8-4      spacetime_1.0-3  spam_0.29-2      tools_2.15.0    
 [9] xts_0.9-2        zoo_1.7-9             

Thanks you,

François

Answer 1

Using this you get all the list of object of package raster

basevals <- ls(pos="package:raster") 

for example

   which(basevals == 'persp')  ## function persp shows up because it is the exported generic.
   141
   which(basevals == 'plot')   ## no function plot
   integer(0)

No when I do this , it works for me:

library(raster)
r <- raster(ncol=10, nrow=10)
values(r) <- runif(ncell(r))
plot(r, main='Raster with 100 cells')

So There is certainly a plot method here. It is not in the previous list “basevals” beacuse it is an S4 method.

To get the plot method of raster package , try this :

 getMethod('plot',signature=signature(x='Raster', y='ANY'))

or more efficiently using

findMethods("plot", "package:raster").