On 11/30/06, Prof Brian Ripley <[EMAIL PROTECTED]> wrote: > On Thu, 30 Nov 2006, Deepayan Sarkar wrote: > > > Hi, > > > > ?interaction says: > > > > See Also: > > > > 'factor'; ':' where 'f:g' is the similar to 'interaction(f, g, > > sep=":")' when 'f' and 'g' are factors. > > > > This is not quite true (or maybe 'similar' is the operative word), since: > > > >> f <- factor(1:3); g <- factor(letters[1:3]) > >> levels(f:g) > > [1] "1:a" "1:b" "1:c" "2:a" "2:b" "2:c" "3:a" "3:b" "3:c" > >> levels(interaction(f, g, sep = ":")) > > [1] "1:a" "2:a" "3:a" "1:b" "2:b" "3:b" "1:c" "2:c" "3:c" > > > > Note the different order of the levels. I like the order in f:g better > > (and at least one other person agrees [1] ), but I also want the > > flexibility of having a 'sep' argument. Would it be possible to change > > interaction to allow this? A simple fix that makes interaction behave > > like ":" is to replace > > No, for it also says > > The levels are ordered so the level of the first factor varies > fastest, then the second and so on. This is the reverse of > lexicographic ordering, and differs from ':'. (It is done this > way for compatibility with S.) > > and reversing it would break things. (It does, I tried it a while back.)
Ah, I should have read the help page more carefully. I'll just write a custom version for my use, which is a fairly simple case. -Deepayan > > as.vector(outer(l, lvs, paste, sep = sep)) > > > > with > > > > as.vector(t(outer(l, lvs, paste, sep = sep))) > > > > in interaction. > > > > -Deepayan > > > > [1] http://tolstoy.newcastle.edu.au/R/help/06/08/32638.html ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
