R devel - Jun 2012 - length-0 list as dimnames

Hi,

I'm working on a package and observed a behaviour that was suggested
to be incompatible with the documentation.

The code below:

x <- matrix(1:4, 2)
dimnames(x) <- list()

works just fine. But checking the documentation for dimnames(), it
states that if value is a list "its components are either 'NULL' or
a
character vector with positive length of the appropriate dimension of
x".

Should dimnames() return an error on the example above?

Thank you very much for your attention and time,

benilton

On Jun 5, 2012, at 7:37 PM, Benilton Carvalho wrote:
> Hi,
> 
> I'm working on a package and observed a behaviour that was suggested
> to be incompatible with the documentation.
> 
> The code below:
> 
> x <- matrix(1:4, 2)
> dimnames(x) <- list()
> 
> works just fine. But checking the documentation for dimnames(), it
> states that if value is a list "its components are either
'NULL' or a
> character vector with positive length of the appropriate dimension of
> x".
> 
> Should dimnames() return an error on the example above?
> 
No, from the docs:

     The replacement method for arrays/matrices coerces vector and
     factor elements of ?value? to character, but does not dispatch
     methods for ?as.character?.  It coerces zero-length elements to
     ?NULL?, and a zero-length list to ?NULL?. 

you are using a 0-length list, so it is coerced to NULL.

Cheers,
Simon


> Thank you very much for your attention and time,
> 
> benilton
> 
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