[R] matrix of random variables from a matrix of means and matrix of sd
Rui Barradas
ruipbarradas at sapo.pt
Fri May 24 22:54:22 CEST 2013
Hello,
The first instruction doesn't call rnorm just once but it seems more
appropriate for your problem;
The second instruction calls rnorm just once.
set.seed(59187)
res1 <- replicate(10, matrix(rnorm(4, mean = a, sd = b), ncol = 2))
set.seed(59187)
res2 <- array(rnorm(40, mean = a, sd = b), dim = c(2, 2, 10))
identical(res1, res2) # TRUE
Hope this helps,
Rui Barradas
Em 24-05-2013 20:22, M M escreveu:
> folks,
> if i have a matrix of means:
> a <- matrix(1:4, 2)
> and a matrix of std deviations:
> b <- matrix(5:8, 2)
> and i want to create a matrix X of random variates such that X[i, j] is a draw from normal distribution with mean = a[i, j] and std dev = b[i, j], i think i can do this?
> X <- matrix(rnorm(4, mean = a, sd = b), ncol = 2)
> now if I want to create 10 such matrices, I could possibly do this:
> lapply(1:10, function(x) matrix(rnorm(4, mean = a, sd = b), ncol = 2))
> is there a better way to do this with perhaps just one call to the rnorm() function?
> cheers,
> murali
> [[alternative HTML version deleted]]
>
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