tail(<matrix>) column numbers
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: *) 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.