Hi all, I believe there is an issue with passing NULL to the function I().
class(NULL) # "NULL" (as expected) print(NULL) # NULL (as expected) is.null(NULL) # TRUE (as expected) According to the documentation I() should return a copy of its input with class "AsIs" preprended: class(I(NULL)) # "AsIs" (as expected) print(I(NULL)) # list() (not expected! should be NULL) is.null(I(NULL)) # FALSE (not expected! should be TRUE) So, I() does not behave according to its documentation. In R, it is not possible to give NULL attributes, but I(NULL) attempts to do that nonetheless, using the structure() function. Probably: 1/ structure() should not accept NULL as input since the goal of structure() is to set some attributes, something cannot be done on NULL. 2/ I() could accept NULL, but, as an exception, not set an "AsIs" class attribute on it. This would be in line with the philosophy of the I() function to return an object that is functionally equivalent to the input object. My sessionInfo() returns: > sessionInfo() R version 3.3.2 (2016-10-31) Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows 7 x64 (build 7601) Service Pack 1 locale: [1] LC_COLLATE=German_Switzerland.1252 LC_CTYPE=German_Switzerland.1252 LC_MONETARY=German_Switzerland.1252 LC_NUMERIC=C [5] LC_TIME=German_Switzerland.1252 attached base packages: [1] stats graphics grDevices utils datasets methods base Best regards, Florent ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
