R devel - Jan 2003 - minor error in documentation of pmax in base (PR#2513)

The documentation says, "pmax and pmin take several vectors as
arguments and return a single vector giving the parallel maxima
(or minima) of the vectors."

I discovered that, if you use a matrix or array instead of a
vector, pmax returns a matrix or array, respectively.

This makes pmax and pmin much more useful, and should not be left
to people to discover on their own!

For example:
m1 <- array(1:24,c(2,3,4))
m2 <- array(24:1,c(2,3,4))
pmax(m1,m2)
pmin(m1,m2)

Jon Baron

If I'm not mistaken, matrices and arrays are just vectors with dim
attribute.  so I'm not surprised that pmax and pmin work as they do.  You
get the same answer by the following:

array(pmax(1:24, 24:1), c(2, 3, 4))
array(pmin(1:24, 24:1), c(2, 3, 4))


Cheers,
Andy
> -----Original Message-----
> From: baron@cattell.psych.upenn.edu
> [mailto:baron@cattell.psych.upenn.edu]
> Sent: Friday, January 31, 2003 12:37 PM
> To: r-devel@stat.math.ethz.ch
> Cc: R-bugs@biostat.ku.dk
> Subject: [Rd] minor error in documentation of pmax in base (PR#2513)
> 
> 
> The documentation says, "pmax and pmin take several vectors as
> arguments and return a single vector giving the parallel maxima
> (or minima) of the vectors."
> 
> I discovered that, if you use a matrix or array instead of a
> vector, pmax returns a matrix or array, respectively.
> 
> This makes pmax and pmin much more useful, and should not be left
> to people to discover on their own!
> 
> For example:
> m1 <- array(1:24,c(2,3,4))
> m2 <- array(24:1,c(2,3,4))
> pmax(m1,m2)
> pmin(m1,m2)
> 
> Jon Baron
> 
> ______________________________________________
> R-devel@stat.math.ethz.ch mailing list
> http://www.stat.math.ethz.ch/mailman/listinfo/r-devel
> 
------------------------------------------------------------------------------

> From: Jonathan Baron [mailto:baron@cattell.psych.upenn.edu]
> 
> In a way it is not surprising, but some functions that operate on
> vectors will coerce their outputs into vectors and others won't.
> For example, try
> 
> m1 <- array(1:24,c(2,3,4))
> sort(m1)
> order(m1)
Now that I think a bit more about this example, I'm not sure if I like pmax
and pmin to work as they do now.  What if one does the following:

a1 <- array(1:24, 2:4)
a2 <- array(24:1, 4:2)
pmax(a1, a2)
pmin(a1, a2)

I don't know if there's a "natural" way to dimension the
result in this
case.  Seen from this perspective, my preference would actually be what
sort() and order() do: drop the attribute.  If array is what's intended,
then the user can do that coercion explicitly.

Just my $0.02...
Andy
> 
> It would be nice to say when each of these things will happen.
> 
> For example, in the documentaition for ifelse, it says, "returns
> a value with the same shape as".  This sort of language would be
> helpful.
> 
> Jon
> 
> On 01/31/03 12:42, Liaw, Andy wrote:
> >If I'm not mistaken, matrices and arrays are just vectors with dim
> >attribute.  so I'm not surprised that pmax and pmin work as 
> they do.  You
> >get the same answer by the following:
> >
> >array(pmax(1:24, 24:1), c(2, 3, 4))
> >array(pmin(1:24, 24:1), c(2, 3, 4))
> >
> >
> >Cheers,
> >Andy
> >
> >> -----Original Message-----
> >> From: baron@cattell.psych.upenn.edu
> >> [mailto:baron@cattell.psych.upenn.edu]
> >> Sent: Friday, January 31, 2003 12:37 PM
> >> To: r-devel@stat.math.ethz.ch
> >> Cc: R-bugs@biostat.ku.dk
> >> Subject: [Rd] minor error in documentation of pmax in base 
> (PR#2513)
> >> 
> >> 
> >> The documentation says, "pmax and pmin take several vectors
as
> >> arguments and return a single vector giving the parallel maxima
> >> (or minima) of the vectors."
> >> 
> >> I discovered that, if you use a matrix or array instead of a
> >> vector, pmax returns a matrix or array, respectively.
> >> 
> >> This makes pmax and pmin much more useful, and should not be left
> >> to people to discover on their own!
> >> 
> >> For example:
> >> m1 <- array(1:24,c(2,3,4))
> >> m2 <- array(24:1,c(2,3,4))
> >> pmax(m1,m2)
> >> pmin(m1,m2)
> >> 
> >> Jon Baron
> >> 
> >> ______________________________________________
> >> R-devel@stat.math.ethz.ch mailing list
> >> http://www.stat.math.ethz.ch/mailman/listinfo/r-devel
> >> 
> >
> >-------------------------------------------------------------
> -----------------
> >Notice: This e-mail message, together with any attachments, 
> contains information of Merck & Co., Inc. (Whitehouse 
> Station, New Jersey, USA) that may be confidential, 
> proprietary copyrighted and/or legally privileged, and is 
> intended solely for the use of the individual or entity named 
> on this message.  If you are not the intended recipient, and 
> have received this message in error, please immediately 
> return this by e-mail and then delete it.
> >
> >============================================================>
================> >
> 
> -- 
> Jonathan Baron, Professor of Psychology, University of Pennsylvania
> Home page:            http://www.sas.upenn.edu/~baron
> Psychology webmaster: http://www.psych.upenn.edu/
> R page:               http://finzi.psych.upenn.edu/
> Questionnaires:       http://www.psych.upenn.edu/~baron/qs.html
> 
------------------------------------------------------------------------------