Actually Jeff Laake's can be made even shorter with sapply(mat_list, as.vector)
David C -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Evan Cooch Sent: Thursday, October 9, 2014 7:37 AM To: Evan Cooch; r-help@r-project.org Subject: Re: [R] cbind in a loop...better way? | summary Two solutions proposed -- not entirely orthogonal, but both do the trick. Instead of nesting cbin in a loop (as I did originally -- OP, below), 1\ do.call(cbind, lapply(mat_list, as.vector)) or 2\ sapply(mat_list,function(x) as.vector(x)) Both work fine. Thanks to Jeff Laake (2) + David Carlson (1) for their suggestions. On 10/8/2014 3:12 PM, Evan Cooch wrote: > ...or some such. I'm trying to work up a function wherein the user > passes a list of matrices to the function, which then (1) takes each > matrix, (2) performs an operation to 'vectorize' the matrix (i.e., > given an (m x n) matrix x, this produces the vector Y of length m*n > that contains the columns of the matrix x, stacked below each other), > and then (3) cbinds them together. > > Here is an example using the case where I know how many matrices I > need to cbind together. For this example, 2 square (3x3) matrices: > > a <- matrix(c,0,20,50,0.05,0,0,0,0.1,0),3,3,byrow=T) > b <- matrix(c(0,15,45,0.15,0,0,0,0.2,0),3,3,byrow=T) > > I want to vec them, and then cbind them together. So, > > result <- cbind(matrix(a,nr=9), matrix(b,nr=9)) > > which yields the following: > > [,1] [,2] > [1,] 0.00 0.00 > [2,] 0.05 0.15 > [3,] 0.00 0.00 > [4,] 20.00 15.00 > [5,] 0.00 0.00 > [6,] 0.10 0.20 > [7,] 50.00 45.00 > [8,] 0.00 0.00 > [9,] 0.00 0.00 > > Easy enough. But, I want to put it in a function, where the number and > dimensions of the matrices is not specified. Something like > > Using matrices (a) and (b) from above, let > > env <- list(a,b). > > Now, a function (or attempt at same) to perform the desired operations: > > vec=function(matlist) { > > n_mat=length(matlist); > size_mat=dim(matlist[[1]])[1]; > > result=cbind() > > for (i in 1:n_mat) { > result=cbind(result,matrix(matlist[[i]],nr=size_mat^2)) > } > > return(result) > > } > > > When I run vec(env), I get the *right answer*, but I am wondering if > there is a *better* way to get there from here than the approach I use > (above). I'm not so much interested in 'computational efficiency' as I > am in stability, and flexibility. > > Thanks... > > . > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
