On 4/10/07, Seth Falcon <[EMAIL PROTECTED]> wrote: > "hadley wickham" <[EMAIL PROTECTED]> writes: > > > On 4/10/07, Tony Plate <[EMAIL PROTECTED]> wrote: > >> Aren't you just seeing the effect of drop=TRUE? (at least with the > >> examples you give below -- they all pick out a submatrix with extent one > >> on some dimension) > >> > >> AFAICT, matrices with a list as the underlying data work properly, > > Yes, I guess so, although I'm surprised this is all that useful. My > mental model is that a matrix is a vector with dimension and that as > such all elements are of the same type. When a list is used for the > underlying data, then this is still true in that each element is > itself a list (at least according to vv[i]), but that is less useful > -- even if you figure out to use [[, there is no guarantee what you > will find there: > > vv = c(list(a=list(inner=1), b="foo", c=matrix(1, nrow=2, ncol=2)), > as.list(1:7)) > dim(vv) = c(2, 5)
That's rather a contrived example. In practice, you would create a list containing the same type of objects. eg: library(reshape) models <- stamp(mtcars, vs ~ am, function(df) lm(mpg ~ wt, data=df)) models dimnames(models) summary(models[[1, 1]]) which I think is a valid and useful thing to do (although a little contrived in this example) > > I use this functionality a lot in the reshape package. I would hate > > to see it go! > > > > It would be nice to have some way to remove the [[1]] from vv[1, > > 2][[1]] though. > > For lists, there is no guaranteed structure and so you can't avoid > [[1]] since [1] will return a list and it can contain *anything*. As (many) others have pointed out, vv[[1,2]] works, as I probably should have checked! > What could be useful is the notion of a vector of S4 objects. There > you could ensure they are all the same type. Yes, but I know what I put in my structure. The contract is not enforced by code, but it is enforced by me. Most of the things I'm dealing with are S3 objects, so a S4 templated vector wouldn't be particularly helpful. Hadley ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
