Finding out what keywords are available
I'm summarising a data table using the usual syntax, e.g. dt << summary( by(Group), mean(TrtA, TrtB, TrtC)), and am getting a summary table back in which all the column names are prefixed by the word "mean", e.g. "mean(TrtA)", "mean(TrtB)" etc. That's obviously both logical and informative, but actually I want to retain the original column headings for reasons that aren't worth going into here. I've written a little function to strip out the extraneous text, but I'm doing a lot of this sort of thing and repeatedly having to tidy them up afterwards is a bit of a nuisance. Is there a keyword for use with the summary command which will do this automatically? I can't find one in the manual, but I could easily have overlooked it if it's called something that isn't obvious.
On a general point, how can I get a list of all the available keywords for any particular command? I keep coming across statements in the manual like "Options include...", whereas I'd like to have a comprehensive list at my fingertips - preferably with descriptions of what they all do.
Many thanks.