Re: [R] Create matrix with subset from unlist

Mon, 01 Feb 2010 06:40:01 -0800 

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.ra...@ouce.ox.ac.uk <mailto:muhammad.ra...@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





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