[Rd] Bug in xy.coords() or documentation error?

[Gavin Simpson]

Hi,

I noticed the following problem with xy.coords() in R 2.2.1-patched
(version info at the foot of this email) and R 2.3.0 unstable
(subversion no: r37123):

> xy.coords(x = matrix(1:20, ncol = 2))
Error in xy.coords(x = matrix(1:20, ncol = 2)) :
        argument "y" is missing, with no default
> xy.coords(x = matrix(1:20, ncol = 2), y = NULL)
$x
 [1]  1  2  3  4  5  6  7  8  9 10

$y
 [1] 11 12 13 14 15 16 17 18 19 20

$xlab
[1] "[,1]"

$ylab
[1] "[,2]"

And:

> xy.coords(x = data.frame(x = 1:10, y = 1:10))
Error in xy.coords(x = data.frame(x = 1:10, y = 1:10)) :
        argument "y" is missing, with no default
> xy.coords(x = data.frame(x = 1:10, y = 1:10), y = NULL)
$x
 [1]  1  2  3  4  5  6  7  8  9 10

$y
 [1]  1  2  3  4  5  6  7  8  9 10

$xlab
[1] "x"

$ylab
[1] "y"

... for example.

?xy.coords states:

    x, y: the x and y coordinates of a set of points. Alternatively, a
          single argument 'x' can be provided.

Given that, I would have thought the above examples would have worked
without explicitly passing y = NULL to xy.coords(). However, ?xy,coords
later states:

    If 'y' is 'NULL' and 'x' is a

and the examples all illustrate the use of NULL passed as y.

Is this a documentation error and a single argument x is not allowed, or
is this a bug in the code? Either way, ?xy.coords contradicts itself as
one would expect to be able to pass only x given the statement above.

If this is a bug in the code, a potential workaround appears to be to
change the first line of xy.coords from:

   if (is.null(y)) {

to

   if (missing(y) || is.null(y)) {

but I haven't tested this on anything other than my two examples.

I will file a bug report if my observation is correct - but given all
the erroneous bug reports lately, I thought I'd try my luck here where
an error on my part would not cause the maintainers of the bug tracker
any extra work.

> version
         _
platform i686-pc-linux-gnu
arch     i686
os       linux-gnu
system   i686, linux-gnu
status   Patched
major    2
minor    2.1
year     2006
month    01
day      18
svn rev  37123
language R
> sessionInfo()
R version 2.2.1, 2006-01-18, i686-pc-linux-gnu

attached base packages:
[1] "methods"   "stats"     "graphics"  "grDevices"
[5] "utils"     "datasets"  "base"

All the best,

Gav

-- 
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Gavin Simpson                     [T] +44 (0)20 7679 5522
ENSIS Research Fellow             [F] +44 (0)20 7679 7565
ENSIS Ltd. & ECRC                 [E] gavin.simpsonATNOSPAMucl.ac.uk
UCL Department of Geography       [W] http://www.ucl.ac.uk/~ucfagls/cv/
26 Bedford Way                    [W] http://www.ucl.ac.uk/~ucfagls/
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