Dear list, I've noticed that if a list or a vector is given a class (by class(x) <- "something") then the "selection operator slows down - quite a bit. For example:
lll <- as.list(letters)
system.time({for(ii in 1:200000)lll[-(1:4)]})
user system elapsed 0.48 0.00 0.49
class(lll) <- "foo"
system.time({for(ii in 1:200000)lll[-(1:4)]})
user system elapsed 2.57 0.00 2.58
vvv <- 1:100
system.time({for(ii in 1:200000)vvv[-(1:4)]})
user system elapsed 0.71 0.00 0.72
class(vvv) <- "foo"
system.time({for(ii in 1:200000)vvv[-(1:4)]})
user system elapsed 2.85 0.00 2.87 I guess that what happens is that R looks for a "["-method for for "foo" objects and when such a method is not found, a default "["-method is called? Is that so? What should one do to avoid such a slowdown when wanting to select elements from a list or a vector with a class? Using unclass is one option:
class(vvv) <- "foo"
system.time({for(ii in 1:200000)unclass(vvv)[-(1:4)]})
user system elapsed 0.94 0.00 0.94 Are there better ways? Best regards S?ren PS: I am using R.2.12.2 on windows 7.