[Rd] Issue when calling deparse(substitute(x)) from C with "anonymous" R vectors ?

[Prof Brian Ripley]

This is easy to reproduce in R:

chisq.test(c(1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011),
c(1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1008, 1009, 1010, 1011))

The simple answer is: don't do that.

It is unclear what is a reasonable label to give in such a case: maybe 
simply 'x' and 'y'?

On Thu, 19 Nov 2009, Laurent Gautier wrote:

> Dear list,
>
>
> When calling R from C, what appears like a spurious error can be triggered 
> during the execution of chisq.test(x, y).
>
> This is happening when the following conditions are met:
>
> - x and y are "anonymous" C-level R vectors (they do not have a symbol),
> but they are protected from garbage collection
>
> - x and y are "not too small" (it was experienced as soon as they are longer 
> than 17 elements).
>
>
> The error is
>
> Error in names(dimnames(x)) <- DNAME :
>  'names' attribute [4] must be the same length as the vector [2]
>
> and can be traced to the use of deparse(substitute(x)) and 
> deparse(substitute(y)) in the R code.
>
> What seems to be happening is that the deparse(substitute(x)) call
> gives a character vector of length > 1 as soon as x is "not so small".
>
> To demonstrate this, I am using rpy2 (as the problem was found when using it
> http://sourceforge.net/mailarchive/forum.php?thread_name=4B043CA1.9050500%40salilab.org&forum_name=rpy-list
> ), but it will likely be present in other bridges to R as well.
>
>
> #using R-2.10 and rpy2-2.1.dev
>>>> import rpy2.robjects as robjects
>
>>>> f = robjects.r('''function(x) return(deparse(substitute(x)))''')
>
>>>> tuple(f(robjects.FloatVector(range(17))))
> ('c(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)',)
> # length 1
>>>> tuple(f(robjects.FloatVector(range(18))))
> ('c(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17', ')')
> # length 2 !!
>
>
> Does it seem to others like an issue present in other bridges as well ?
>
>
>
> L.
>
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>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595