Re: [Rd] Re: tail() column numbers

Tony Plate Tue, 13 Jul 2004 09:06:46 -0700

It does seem useful to report original line numbers when tail() is used interactively, but to do this properly, shouldn't it be done in "print" method, rather than by adding row numbers to the data? This is admittedly difficult, because the tail method and the print method are completely separate. One could possibly do this by adding an additional attribute to the object returned by tail (which presumably would be lost on further subsetting), and modifying the relevant print methods to use such information when it is present.

I suspect that the trouble may not be worth the effort in this particular case, but nonetheless it still may be worth thinking about as an example of the general problem of how reconcile what is convenient for interactive use with what is convenient for programming use. (Other examples of which have resulted in permanent defects (IMHO) of the language, such as partial matching for "$" and the default drop=T in subsetting.)

-- Tony Plate

At Monday 01:27 PM 7/12/2004, Patrick Burns wrote:

I give it my vote as well.

Pat


Warnes, Gregory R wrote:

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:[EMAIL PROTECTED]
Sent: Monday, July 12, 2004 8:06 AM
To: Patrick Burns
Cc: Martin Maechler; Warnes, Gregory R; Prof Brian Ripley; Kevin Wright;
[EMAIL PROTECTED]; Peter Dalgaard
Subject: Re: tail(<matrix>) column numbers


On Sun, 11 Jul 2004 12:06:44 +0100, Patrick Burns
<[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>
  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.

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Re: [Rd] Re: tail() column numbers

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