In R 3.3.0 (also in R 2.7.2), the documentation on 'factor', in "Details" section, has this statement. 'factor(x, exclude = NULL)' applied to a factor is a no-operation unless there are unused levels: in that case, a factor with the reduced level set is returned.
It is not true for a factor 'x' that has NA. In that case, if levels of 'x' doesn't contain NA, factor(x, exclude = NULL) adds NA as a level. If levels of a factor 'x' doesn't contain NA, factor(x) is a no-operation if all levels are used. In R 3.3.0 (also in R 3.1.3), for a named integer 'x', factor(x) has names and as.factor(x) doesn't. It would be better if the behavior on names were matched. > x <- integer(1) > names(x) <- "a" > names(factor(x)) [1] "a" > names(as.factor(x)) NULL > sessionInfo() R version 3.3.0 (2016-05-03) Platform: i386-w64-mingw32/i386 (32-bit) Running under: Windows XP (build 2600) Service Pack 2 locale: [1] LC_COLLATE=English_United States.1252 [2] LC_CTYPE=English_United States.1252 [3] LC_MONETARY=English_United States.1252 [4] LC_NUMERIC=C [5] LC_TIME=English_United States.1252 attached base packages: [1] stats graphics grDevices utils datasets methods base loaded via a namespace (and not attached): [1] tools_3.3.0 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
