[Rd] Re: tail(<matrix>) column numbers

[Duncan Murdoch]

If efficiency is a concern, an "add.row.names=TRUE" option could be
added; users who didn't want the overhead would set this to FALSE.

Duncan Murdoch

On Fri, 9 Jul 2004 10:35:42 +0200, Martin Maechler
<maechler at stat.math.ethz.ch> wrote :

>>>>>> "PatBurns" == Patrick Burns <pburns at 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.
>
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