Re: R-alpha: batch mode and interactions

Ross Ihaka (
Thu, 6 Jun 1996 10:41:35 +1200

Date: Thu, 6 Jun 1996 10:41:35 +1200
From: Ross Ihaka <>
Message-Id: <>
Subject: Re: R-alpha: batch mode and interactions
In-Reply-To: <>

Bill Venables writes:
 > Rather than use a "." for interactions would you consider using a
 > ":" to reflect the (low level) operator that creates them?

I'm a little worried that a:b is not a valid name, but I must admit
to not knowing whether this matters or not.  It would be a trivial
change (as would leaving out the "." a la S).

 > Of course even this does not go far enough.  There are two types of
 > "interaction" between factors, the "A:B" type and the "B %in% A"
 > type which are equivalent in abstract terms to "B + A:B".  I think
 > labelling is potentially very important in this area but doing it
 > justice is going to generate labels far too long.  You can't win.

This is something I have neglected, but think it will not be too hard
to change the terms function so that this will work.  It would mean
that y~a*b/c would produce the terms a, b ,a:b, c%in%(a*b).
I think I will squeeze the spaces from around the %in% to save space.

By the by.  Our Mac programmer is back and so we are back on track
for ports to the 68k and PPC Macs.

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