[R] Question about NULL matrix? Can I define a NULL matrix in R?

[Rolf Turner]

On 11/08/11 13:11, David Winsemius wrote:
>
> On Aug 10, 2011, at 8:23 PM, Andra Isan wrote:
>
>> Hi All,
>> I would like to create a matrix in R but I dont know the size of my 
>> matrix. I only know the size of the columns but not the size of the 
>> rows. So, is there any way to create a dynamic matrix of size NULL by 
>> n_cols? and then add to that matrix?
>> I know for a vector, I can do this: x= NULL but is there any way to 
>> do the same for a matrix as well?
>
> No. You cannot make an R matrix without knowing the number of rows. By 
> definition an R matix has two integer dimensions. Alternatives: You 
> can rbind to an existing matrix, or you can make a larger than 
> necessary matrix filled with NA's and then fill and later extract a 
> subset of the rows.
>

Wrong-oh, David.  :-) Check this out:

 > m <- matrix(0,nrow=0,ncol=5)
 > m
     [,1] [,2] [,3] [,4] [,5]

     cheers,

         Rolf