[Rd] Question about colnames behavior

Martin Maechler maechler at stat.math.ethz.ch
Mon Oct 3 15:04:00 CEST 2005

>>>>> "BDR" == Prof Brian Ripley <ripley at stats.ox.ac.uk>
>>>>>     on Mon, 3 Oct 2005 09:44:47 +0100 (BST) writes:

    BDR> On Mon, 3 Oct 2005, Martin Maechler wrote:
    >>>>>>> "Erich" == Erich Neuwirth <erich.neuwirth at univie.ac.at>
    >>>>>>> on Sun, 02 Oct 2005 09:39:36 +0200 writes:
    Erich> The following code
    Erich> zzz<-1:10
    Erich> dim(zzz)<-10
    Erich> rownames(zzz)
    Erich> colnames(zzz)
    Erich> yields NULL for the rownames and colnames calls.
    Erich> Let us set rownames
    Erich> rownames(zzz)<-1:10
    Erich> Now rownames(zzz) returns the expected result, but colnames(zzz)
    Erich> produces an error:
    Erich> Error in dn[[2]] : subscript out of bounds
    Erich> So given a onedimensional structure the return behavior of colnames
    Erich> is different depending on the fact if rownames are set or not.
    Erich> Should the behavior of colnames be changed to make the result
    Erich> independent from this fact?
    >> yes, thank you, Erich.
    >> It should give an error also in the 1st  case which is
    >> BTW identical to
    >> zzz <- array(1:10)

    BDR> Not according to my reading of the help, which says

      >> The extractor functions try to do something sensible for any
      >> matrix-like object 'x'.  If the object has 'dimnames' the first
      >> component is used as the row names, and the second component (if
      >> any) is used for the col names.

    BDR> and reading on, I think it should give NULL in both cases.  You could 
    BDR> argue that a 1D array is not `matrix-like', but that seems a narrow 
    BDR> interpretation (especially as rownames does work for such arrays).

I was lead to my conclusion by the same help page, reading

 >> Arguments:
 >>    x: a matrix-like R object, with at least two dimensions for 'colnames'.

from which I concluded an error was appropriate for 'colnames'
when 'x' doesn't have two dimensions.

If we adopt your proposal (NULL in any case), we should
definitely also fix that paragraph...


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