Debugging this issue: https://github.com/Rdatatable/data.table/issues/2008
We have custom class 'IDate' which inherits from 'Date' (it just forces integer storage for efficiency, hence, I). The concatenation done by rbind, however, breaks this and returns a double: library(data.table) DF = data.frame(date = as.IDate(Sys.Date())) storage.mode(rbind(DF, DF)$date) # [1] "double" This is specific to base::rbind (data.table's rbind returns an integer as expected); in ?rbind we see: The method dispatching is not done via UseMethod(), but by C-internal dispatching. Therefore there is no need for, e.g., rbind.default. The dispatch algorithm is described in the source file (‘.../src/main/bind.c’) as 1. For each argument we get the list of possible class memberships from the class attribute. 2. *We inspect each class in turn to see if there is an applicable method.* 3. If we find an applicable method we make sure that it is identical to any method determined for prior arguments. If it is identical, we proceed, otherwise we immediately drop through to the default code. It's not clear what #2 means -- an applicable method *for what*? Glancing at the source code would suggest it's looking for rbind.IDate: https://github.com/wch/r-source/blob/trunk/src/main/bind.c#L1051-L1063 const char *generic = ((PRIMVAL(op) == 1) ? "cbind" : "rbind"); // should be rbind here const char *s = translateChar(STRING_ELT(classlist, i)); // iterating over the classes, should get to IDate first sprintf(buf, "%s.%s", generic, s); // should be rbind.IDate but adding this method (or even exporting it) is no help [ simply defining rbind.IDate = function(...) as.IDate(NextMethod()) ] Lastly, it appears that as.Date.IDate is called, which is causing the type conversion: debug(data.table:::as.Date.IDate) rbind(DF, DF) # launches debugger x # [1] "2019-05-26" <-- singleton, so apparently applied to DF$date, not c(DF$date, DF$date) undebug(data.table:::as.Date.IDate) I can't really wrap my head around why as.Date is being called here, and even allowing that, why the end result is still the original class [ class(rbind(DF, DF)$date) == c('IDate', 'Date') ] So, I'm beginning to think this might be a bug. Am I missing something? [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
