Dear R-help, I am attempting to set the "Summary" group generic function for my S4 class. Using the standard arguments, this is easy. The function returns the result of the generic for every element in a list: setClass("TestClass", representation(elements = "list")) tc <- new("TestClass", elements = list(a = 1:5, b = 6:20)) setMethod("Summary", "TestClass", function(x, ..., na.rm) sapply(x@elements, .Generic, ..., na.rm = na.rm)) max(tc) # c(a = 5, b = 20) However if I try to add a new argument ("k" in this example) I am unable to access the ".Generic" function. (Note: R restart required to reload the group generic definition): setMethod("Summary", "TestClass", function(x, k, ..., na.rm) k * sapply(x@elements, .Generic, ..., na.rm = na.rm)) max(tc, -1) # Error in match.fun(FUN) : object '.Generic' not found The help for ?setMethod covers this briefly with "Roughly, if the generic has ... as one of its arguments, then the method may have extra formal arguments, which will be matched from the arguments matching ... in the call to ‘f’." Am I misunderstanding / misusing it? I see the same results on R version 2.12.1 (2010-12-16) Platform: i486-pc-linux-gnu (32-bit) and R version 2.13.0 (2011-04-13) Platform: i386-pc-mingw32/i386 (32-bit) Many thanks, Andrew ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.