>-----Original Message----- >From: [EMAIL PROTECTED] >[mailto:[EMAIL PROTECTED] On Behalf Of Prof >Brian Ripley >Sent: Friday, June 27, 2003 12:11 PM >To: Marc Schwartz >Cc: [EMAIL PROTECTED]; 'Nick Bond' >Subject: RE: [R] dropping factor levels in subset > > >Re: [, drop=TRUE} for factors > >It's been in S-PLUS (but not S I believe) for a long time, >probably since >before 1994: it is in S+3.4, 1996 vintage. > >It appears to have been added to R around August 1998. > >Yes, Frank Harrell argues for the default to be true and I believe his >Hmisc package overrides this. Although less unsafe than it >used to be (a >lot more consistency checking of factor levels has been added) >it is still >I believe undesirable. The argument `drop.unused.levels' to >model.frame >will usually do all that is required. (That's another thing that is >very-little known.)
Thanks for the clarifications. SNIP >> I now note that for factor objects, this is included in MASS 4 (pg >> 19), whereas it is a footnote in MASS 3 (pg 20) and I could not find >> it in MASS 1 (I don't have a copy of MASS 2 to review). It is also a >> footnote in S Programming (pg 14). Not sure if any >significance should >> be attached to being a footnote versus being in the body of >the text. > >None. OK. I initially had the impression that it may have been either chronologically associated with the addition of this method for factors or the greater emphasis on R in MASS 4, since it moved from a footnote to the body. I was wrong. Also, I realized a typo in the MASS 4 page number I had above, it should be 16. Regards, Marc ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help