On 03/02/2010 6:49 PM, William Dunlap wrote:
-----Original Message-----
From: h.wick...@gmail.com [mailto:h.wick...@gmail.com] On
Behalf Of Hadley Wickham
Sent: Wednesday, February 03, 2010 3:38 PM
To: William Dunlap
Cc: r-devel@r-project.org
Subject: Re: [Rd] Proposal unary - operator for factors
It wouldn't make sense in the context of
vector[-factor]
True, but that doesn't work currently so you wouldn't lose anything.
However, it would make a certain class of problem that used to throw
errors become silent.
Wouldn't it be better to allow order's decreasing argument
to be a vector with one element per ... argument? That
would work for numbers, factors, dates, and anything
else. Currently order silently ignores decreasing[2] and
beyond.
The problem is you might want to do something like order(a, -b, c, -d)
Currently, for numeric a you can do either
order(-a)
or
order(a, decreasing=FALSE)
For nonnumeric types like POSIXct and factors only
the latter works.
Under my proposal your
order(a, -b, c, d)
would be
order(a, b, c, d, decreasing=c(FALSE,TRUE,FALSE,TRUE))
and it would work for any ordably class without modifications
to any classes.
Why not use
order(a, -xtfrm(b), c, -xtfrm(d))
??
Duncan Murdoch
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