tail(<matrix>) column numbers

I also vote for the 'helpful' addition on row numbers based on the original
matrix when no row names are present, with an optional argument to prevent
this behaviour.

-G

 

-----Original Message-----
From: Duncan Murdoch [mailto:dmurdoch@pair.com]
Sent: Monday, July 12, 2004 8:06 AM
To: Patrick Burns
Cc: Martin Maechler; Warnes, Gregory R; Prof Brian Ripley; 
Kevin Wright;
r-devel@stat.math.ethz.ch; Peter Dalgaard
Subject: Re: tail(<matrix>) column numbers


On Sun, 11 Jul 2004 12:06:44 +0100, Patrick Burns
<pburns@pburns.seanet.com> wrote :

   

I disagree with Martin's assertion that "tail" is not useful
for programming.  It has a few features relative to the
do-it-yourself approach:
     

Me too actually.  I think tail() has two uses, interactive and
programmatic.  I think it would be better for interactive use if 
the row names were added, and only slightly worse for programmatic use
if an option were given to turn them off.

In interactive use, I find it unhelpful to be told that something is
in row 3 when it's really in row 47.

Duncan Murdoch

   

*)  It compactly makes the intention clear.
*)  It automatically handles cases where there may be
either a vector or a matrix.
*)  It handles cases where there is less data than is being
sought (which may or may not be a good thing).

"tail" of functions is what is definitely intended for interactive
use.

Pat

Martin Maechler wrote:

     

"PatBurns" == Patrick Burns <pburns@pburns.seanet.com>
  on Tue, 27 Jan 2004 14:20:30 +0000 writes:
          

                 

[more than half a year ago]

  PatBurns> Duncan Murdoch wrote:

 .............

  DM> One other one I'll look at:
  DM> 
  DM> If a matrix doesn't have row names, I might add names
  DM> like '[nn,]' to it, so I get results like

    R> x <- matrix(1:100,ncol=2)
    R> tail(x)
 Rout>       [,1] [,2]
 Rout> [45,]   45   95
 Rout> [46,]   46   96
 Rout> [47,]   47   97
 Rout> [48,]   48   98
 Rout> [49,]   49   99
 Rout> [50,]   50  100
 Rout> 
  DM> instead of the current

    R> tail(x)
 Rout>      [,1] [,2]
 Rout> [1,]   45   95
 Rout> [2,]   46   96
 Rout> [3,]   47   97
 Rout> [4,]   48   98
 Rout> [5,]   49   99
 Rout> [6,]   50  100

  DM> I just want to be careful that this doesn't mess up
  DM> something else.
  DM> 
  DM> Duncan Murdoch


  PatBurns> I think this could be being too "helpful".  Using
  PatBurns> tail on a matrix may often be done in a program so
  PatBurns> I think leaving things as they come is the best
  PatBurns> policy.

I tend to disagree, and would like to have us think about it
again:

1)  Duncan's proposal was to only add row names *when* 
       

there are none.
   

2)  Pat is write that tail() for matrices maybe used not 
       

only interactively
   

  and help(tail)'s "Value:" section encourages this to 
       

some extent.
   

  However, how can adding column names to such a 
       

matrix-tail be harmful?
   

  Well, only in the case where the tail is quite large, the
  added dimnames add unneeded memory and other overhead when
  dealing with that matrix.

But I think, programmers/users caring about efficient code
wouldn't use tail(<matrix>) in their function code, would they?

In conclusion, I'd still argue for following Duncan's proposal,
maybe adding a \note{.} to head.Rd stating that these functions
were meant for interactive use, and for "programming", we'd
rather recommend the direct  (n-k+1):n indexing.




       

LEGAL NOTICE
Unless expressly stated otherwise, this message is confidential and may be privileged. It is intended for the addressee(s) only. Access to this E-mail by anyone else is unauthorized. If you are not an addressee, any disclosure or copying of the contents of this E-mail or any action taken (or not taken) in reliance on it is unauthorized and may be unlawful. If you are not an addressee, please inform the sender immediately.