[R] Create matrix with subset from unlist

[Muhammad Rahiz]

Hello all,

Thanks for all your replies.

Usually, when I make a post to the R-mailing list, I would keep on 
trying to get the solution myself rather than waiting for one. At times, 
I was able to derive my own solution. This would explain why my solution 
and that of Dennis's produces the same result - not that I totally 
ignore the method of his...

Anyway, I did manage to create the matrix I require. But there is still 
the recurring problem of " (list) object cannot be coerced to type 
'double'  " in further analysis using the dataset. I thought I  could 
resolve it by changing converting to matrix. Seems not.

Given, the following, is there any other way I can define y other that 
using list()? Seems that producing a list of matrices does not work.


y <-
for (i in 1:32){
y[[i]] <- matrix(xx[c(1:4)],2,2)
}


Muhammad 





Dennis Murphy wrote:
> Correct me if I'm wrong, but isn't this the solution I gave??
>
> On Fri, Jan 29, 2010 at 9:43 AM, Muhammad Rahiz 
> <muhammad.rahiz at ouce.ox.ac.uk <mailto:muhammad.rahiz at ouce.ox.ac.uk>> 
> wrote:
>
>     Thanks David & Dennis,
>
>     I may have found something.
>
>     Given that the object xx is the product of unlist(x), to create a
>     2x2 matrix with subsets, I could do,
>
>     > y <- matrix(xx[c(1:4)], 2, 2).
>
> First object named y...
>  
>
>     This returns,
>
>
>         [,1]  [,2]
>     [1,] -27.3  14.4
>     [2,]  29.0 -38.1
>
>     If I do,
>
>     > y2 <- matrix(xx[c(5:8)],2,2)
>
>
> second object named y2
>
>     it returns,
>
>
>         [,1] [,2]
>     [1,]  14.4 29.0
>     [2,] -38.1 -3.4
>
>
> And I presume you want to do the same with the remaining 30 matrices,
> assigning them to different objects. That is *precisely* what my solution
> provided. Run it, observe the results and tell me what it is that 
> differs from
> what you want, because I don't see it.
>
> Dennis
>  
>
>     The results are exactly what I want to achieve.
>
>     The question is, how can I incorporate the increment in a for loop
>     so that it becomes
>
>     c(1:4)
>     c(5:8)
>     c(9:12) and so on
>
>     How should I modify this code?
>
>     y <-            # typeof ? for (i in 1:32){
>     y[[i]] <- matrix(xx[c(1:4)],2,2)
>     }
>
>
>     Muhammad
>
>
>     David Winsemius wrote:
>
>         On Jan 29, 2010, at 9:45 AM, Dennis Murphy wrote:
>
>          
>
>             Hi:
>
>             The problem, I'm guessing, is that you need to assign each
>             of the  matrices
>             to an object.
>             There's undoubtedly a slick apply family solution for this
>             (which I  want to
>             see, BTW!),
>                
>
>
>         I don't have a method that would assign names but you could
>         populate  an array of sufficient size and dimension. I
>         populated a three-element  list with his data:
>
>          > dput(x)
>         list(structure(list(V1 = c(-27.3, 29), V2 = c(14.4, -38.1)),
>         .Names =  c("V1",
>         "V2"), class = "data.frame", row.names = c("1", "2")),
>         structure(list(
>             V1 = c(14.4, -38.1), V2 = c(29, -3.4)), .Names = c("V1",
>         "V2"), class = "data.frame", row.names = c("1", "2")),
>         structure(list(
>             V1 = c(29, -3.4), V2 = c(-38.1, 55.1)), .Names = c("V1",
>         "V2"), class = "data.frame", row.names = c("1", "2")))
>
>          > xx <- array( , dim=c(2,2,3))
>
>          > xx[,,1:3] <- sapply(x, data.matrix)
>          > xx
>         , , 1
>
>               [,1]  [,2]
>         [1,] -27.3  14.4
>         [2,]  29.0 -38.1
>
>         , , 2
>
>               [,1] [,2]
>         [1,]  14.4 29.0
>         [2,] -38.1 -3.4
>
>         , , 3
>
>              [,1]  [,2]
>         [1,] 29.0 -38.1
>         [2,] -3.4  55.1
>
>         Without the more complex structure ready to accept the 2x2
>         arrays I  got this:
>
>          > sapply(x, data.matrix)
>               [,1]  [,2]  [,3]
>         [1,] -27.3  14.4  29.0
>         [2,]  29.0 -38.1  -3.4
>         [3,]  14.4  29.0 -38.1
>         [4,] -38.1  -3.4  55.1
>
>          
>
>