[R] creating matrices from lists

[David Winsemius]

On Sep 20, 2010, at 10:12 PM, Gregory Ryslik wrote:

> Hi,
>
> I have a list of 5 main elements where each main element has 247  
> atomic entries either 0 or 1. I need to get this into a 247x5 matrix  
> so I do "do.call(cbind, mylist)".  However, it renumbers 0 to a 1  
> and the 1 to a 2 so that my matrix is filled with 1's and 2's.
>

If I had such a problem I would see if this were more effective:

matrix(unlist(mylist), length(mylist[[1]]) )

(There is the column major order default of R matrices.)

> I understand I can fix it in this case by doing a replace but I  
> would like to avoid that step. Further, sometimes, my list entries  
> will be from 0 to n. I don't want to have to always renumber all the  
> possibilities.
>
> I'm not quite sure why this is going on because when I build the  
> following: l <- list(c(1,2,3),c(1,2,3),c(1,2,3))
> and execute do.call(cbind, l) it works just fine and there is no  
> renumbering!

I wouldn't have expected it either, but you only provided an example  
of what did work. My attempt at reproducing your problem also failed:

 > ll <- list(a=c(1,0,1,1,0), b=c(0,1,0,0,1)  )
 > do.call(cbind, ll)
      a b
[1,] 1 0
[2,] 0 1
[3,] 1 0
[4,] 1 0
[5,] 0 1

I am wondering if you are dealing with factors and have not looked at  
your "list" with str(). Haven't tried my method above to see what  
would happen in tat instance.



>
> Thanks,
> Greg
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT