R devel - Oct 2005 - Small issue with R's C API

Consider the R code:
mat <- matrix(seq(1,20),4,5)
is.matrix(mat) # gives TRUE
is.vector(mat) # gives FALSE

On the other hand, if mat is passed through the .Call interface the
corresponding SEXP (call it smat) satisfies
isMatrix(smat)   // TRUE
isVector(smat)  // TRUE

Consequently, you cannot distinguish matrices from vectors. Looking
at the dim attribute of a vector doesn't help because this is garbage.

Dominick

This is nothing to do with the C API: isVector and isMatrix are not part 
of the API (see Writing R Extensions for what it is).  That's the
`issue'
here.

On Tue, 25 Oct 2005, Dominick Samperi wrote:
> Consider the R code:
> mat <- matrix(seq(1,20),4,5)
> is.matrix(mat) # gives TRUE
> is.vector(mat) # gives FALSE
>
> On the other hand, if mat is passed through the .Call interface the
> corresponding SEXP (call it smat) satisfies
> isMatrix(smat)   // TRUE
> isVector(smat)  // TRUE
>
> Consequently, you cannot distinguish matrices from vectors. Looking
> at the dim attribute of a vector doesn't help because this is garbage.
You can look to see if it has a dim attribute ... you could also look at 
the C code for is.vector.

Where did you find a definition of isVector?  There is one in the comments 
in src/main/util.c.  It is not as you seem to be assuming a C analogue of
is.vector.

-- 
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)
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