So, its easy enough to create a random matrix, using something like (say)
matrix(rnorm(4),2,2)
which generates a (2x2) matrix with random N(0,1) in each cell.
But, what I need to be able to do is create a 'list' of such random
matrices, where the length of the list (i.e., the number of said random
matrices I store in the list) is some variable I can pass to the
function (or loop).
I tried the obvious like
hold <- list()
for (i in 1:5) {
hold[[i]] <- matrix(rnorm(4),2,2)
}
While this works, it seems inelegant, and I'm wondering if there is a
better (more efficient) way to accomplish the same thing -- perhaps
avoiding the loop.
Thanks in advance...
> On Nov 9, 2016, at 12:32 PM, Evan Cooch <evan.cooch at gmail.com> wrote: > > So, its easy enough to create a random matrix, using something like (say) > > matrix(rnorm(4),2,2) > > which generates a (2x2) matrix with random N(0,1) in each cell. > > But, what I need to be able to do is create a 'list' of such random matrices, where the length of the list (i.e., the number of said random matrices I store in the list) is some variable I can pass to the function (or loop). > > I tried the obvious like > > hold <- list() > for (i in 1:5) { > hold[[i]] <- matrix(rnorm(4),2,2) > } > > > While this works, it seems inelegant, and I'm wondering if there is a better (more efficient) way to accomplish the same thing -- perhaps avoiding the loop. > > Thanks in advance...Hi, See ?replicate Example: ## Create a list of 5 2x2 matrices> replicate(5, matrix(rnorm(4), 2, 2)), , 1 [,1] [,2] [1,] -0.1695775 1.0306685 [2,] 0.1636667 0.1044762 , , 2 [,1] [,2] [1,] -0.3098566 2.1758363 [2,] -0.8029768 0.9697776 , , 3 [,1] [,2] [1,] 0.5702972 0.7165806 [2,] -0.9731331 0.8332827 , , 4 [,1] [,2] [1,] -0.8089588 0.09195256 [2,] -0.2026994 0.67545827 , , 5 [,1] [,2] [1,] 0.5093008 -0.3097362 [2,] 0.6467358 0.3536414 Regards, Marc Schwartz [[alternative HTML version deleted]]
Hello, Try using ?lapply, its return value is a list. Note however that the *apply functions are loops in disguise. There's nothing wrong with your solution to the problem, but it's true that most R users find lapply more elegant, like you say. hold <- lapply(1:5, function(x) matrix(rnorm(4),2,2) ) Hope this helps, Rui Barradas Em 09-11-2016 18:32, Evan Cooch escreveu:> So, its easy enough to create a random matrix, using something like (say) > > matrix(rnorm(4),2,2) > > which generates a (2x2) matrix with random N(0,1) in each cell. > > But, what I need to be able to do is create a 'list' of such random > matrices, where the length of the list (i.e., the number of said random > matrices I store in the list) is some variable I can pass to the > function (or loop). > > I tried the obvious like > > hold <- list() > for (i in 1:5) { > hold[[i]] <- matrix(rnorm(4),2,2) > } > > > While this works, it seems inelegant, and I'm wondering if there is a > better (more efficient) way to accomplish the same thing -- perhaps > avoiding the loop. > > Thanks in advance... > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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.
Hello, I also thought of replicate() but it creates an 2x2x5 array, not a list. Maybe it's all the same for the OP. Rui Barradas Em 09-11-2016 18:41, Marc Schwartz escreveu:> >> On Nov 9, 2016, at 12:32 PM, Evan Cooch <evan.cooch at gmail.com> wrote: >> >> So, its easy enough to create a random matrix, using something like (say) >> >> matrix(rnorm(4),2,2) >> >> which generates a (2x2) matrix with random N(0,1) in each cell. >> >> But, what I need to be able to do is create a 'list' of such random matrices, where the length of the list (i.e., the number of said random matrices I store in the list) is some variable I can pass to the function (or loop). >> >> I tried the obvious like >> >> hold <- list() >> for (i in 1:5) { >> hold[[i]] <- matrix(rnorm(4),2,2) >> } >> >> >> While this works, it seems inelegant, and I'm wondering if there is a better (more efficient) way to accomplish the same thing -- perhaps avoiding the loop. >> >> Thanks in advance... > > > Hi, > > See ?replicate > > Example: > > ## Create a list of 5 2x2 matrices > >> replicate(5, matrix(rnorm(4), 2, 2)) > , , 1 > > [,1] [,2] > [1,] -0.1695775 1.0306685 > [2,] 0.1636667 0.1044762 > > , , 2 > > [,1] [,2] > [1,] -0.3098566 2.1758363 > [2,] -0.8029768 0.9697776 > > , , 3 > > [,1] [,2] > [1,] 0.5702972 0.7165806 > [2,] -0.9731331 0.8332827 > > , , 4 > > [,1] [,2] > [1,] -0.8089588 0.09195256 > [2,] -0.2026994 0.67545827 > > , , 5 > > [,1] [,2] > [1,] 0.5093008 -0.3097362 > [2,] 0.6467358 0.3536414 > > > Regards, > > Marc Schwartz > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. >
> On Nov 9, 2016, at 12:41 PM, Marc Schwartz <marc_schwartz at me.com> wrote: > > >> On Nov 9, 2016, at 12:32 PM, Evan Cooch <evan.cooch at gmail.com> wrote: >> >> So, its easy enough to create a random matrix, using something like (say) >> >> matrix(rnorm(4),2,2) >> >> which generates a (2x2) matrix with random N(0,1) in each cell. >> >> But, what I need to be able to do is create a 'list' of such random matrices, where the length of the list (i.e., the number of said random matrices I store in the list) is some variable I can pass to the function (or loop). >> >> I tried the obvious like >> >> hold <- list() >> for (i in 1:5) { >> hold[[i]] <- matrix(rnorm(4),2,2) >> } >> >> >> While this works, it seems inelegant, and I'm wondering if there is a better (more efficient) way to accomplish the same thing -- perhaps avoiding the loop. >> >> Thanks in advance... > > > Hi, > > See ?replicate > > Example: > > ## Create a list of 5 2x2 matricesSorry, correction on my reply. I copied the wrong output, It should be:> replicate(5, matrix(rnorm(4), 2, 2), simplify = FALSE)[[1]] [,1] [,2] [1,] 0.9700486 1.4249251 [2,] 0.7621312 0.8267747 [[2]] [,1] [,2] [1,] 0.4517927 0.2047509 [2,] 0.6336959 -0.6028124 [[3]] [,1] [,2] [1,] 0.6468823 0.4268734 [2,] 0.1664907 0.3905180 [[4]] [,1] [,2] [1,] -0.3170839 -1.0113201 [2,] -1.5356600 0.9658132 [[5]] [,1] [,2] [1,] -1.1937503 -0.2653502 [2,] 0.9319919 0.1780254 The 'simplify' argument should be FALSE, so that an array is not created. Regards, Marc Schwartz [[alternative HTML version deleted]]