[R] Workings of model.frame.default and [.

David Kane <David Kane a296180 at agate.fmr.com
Tue Jul 30 11:55:17 CEST 2002

Frank E Harrell Jr writes:
> Thanks again, and I'll put in one more plug for [.factor to be modified so
> that if a system option 'drop.unused.levels' is TRUE (i.e., NOT by default)
> drop=TRUE is assumed unless drop=FALSE is explicitly stated by the user.
> Then I can dispose of my local [.factor once and for all.
I'll second this notion. Although a wiser man than I would hesitate to comment
on the relationship between R-core and Professor Harrell, it would seem a nice
thing for R-core to do to "Welcome Aboard" Professor Harrell to the land of R,
given his many contributions (Hmisc, Design, et cetera) to the S language over
the years.

Of course, there is probably some deep design issue why this is hard to do or
some (obvious) statistical reason why one would not want R to provide this much
"rope" to unsophisticated users. If so, I would enjoy being educated about the
issues involved.

In my own small corner of the world, I would use such an option. One of the
biggest complaints that my colleagues have about dataframes is precisely this
behavior. It was also one of my own biggest confusions when starting with S+.

Just my 2 cents,

Dave Kane
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