If I start an R session with a previously saved .RData that has S4
objects in it, there are times when the associated package loads when
I use (or mention) the object, and times when it doesn't. For example:
> dim(casesIn)
NULL
> library(sp)
> dim(casesIn)
[1] 726 22
- because casesIn is a SpatialPointsDataFrame. But if I try and plot
it (starting from scratch again), it loads the sp package:
> plot(casesIn)
Loading required package: sp
- and then falls over:
Error in as.double(y) :
cannot coerce type 'S4' to vector of type 'double'
- which is the error you get from plot.default(casesIn).
Trying plot(casesIn) again then works, producing a point map. Why
doesn't it work the first time?
dim(casesIn) never triggers a library(sp) call:
> dim(casesIn)
NULL
- so do it manually:
> library(sp)
> dim(casesIn)
[1] 726 22
- I guess it must depend on whether its a generic of S3 or S4 flavour
and/or the current phase of the moon.
I can't find any information about this behaviour, and I can't think
of a good query to search for it either. I keep hitting the 'autoload'
documentation, which seems to be something completely different.
R 2.10.1 on Linux - can't see anything relevant in the latest NEWS file.
Barry
