Full_Name: Allan Stokes Version: 28.1 OS: XP Submission from: (NULL) (24.108.0.245)
I'm trying to use package HDF5 and have discovered some round-trip errors: save, load, save is not idempotent. I started digging into the type system to figure out what type graffiti is fouling this up. Soon I discovered that comparisons with NULL produce zero length vectors, which I hadn't known was possible, and I started to wonder about the properties of zero length objects. L0 <- logical (0) dim(L0) <- c(0) # OK dim(L0) <- c(1) # error dim(L0) <- c(0,1) # OK dim(L0) <- c(0,-1) # OK dim(L0) <- c(0,3.14) # OK, c(0,3) results dim(L0) <- c(0,FALSE) # OK c(0,0) results dim(L0) <- c(0,NA) # OK dim(L0) <- c(1,NA) # error dim(L0) <- c(1,NA,NA) # OK, SURPRISE!! NA*NA is normally NA, but in the test for dim() assignment, it appears that NA*NA == 0, which is then allowed. If the list contains more than one NA elements, the product seems to evaluate to zero. I can see making a case for 0*NA == 0 in this context, but not for NA*NA == 0. As an aside, I'm not sure why 0*NA does not equal 0 in general evaluation, unless NA is considered to possibly represent +/-inf. ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
