On Sun, 11 Jul 2010, Robin Jeffries wrote:
I know this is a simple question, but I have yet to master the apply
statements. Any help would be appreciated.
You don't want to use apply() here: rbinom is vectorized. However, you
cannot use mat$x on a matrix, and the cbind() gave you a matrix
anyway. So something like
mat <- data.frame(p=runif(10,0,1), n=rep(1:5))
mat$x <- with(mat, rbinom(10, n, p))
is the idiomatic way to do it.
As an example of using apply and a matrix:
mat <- cbind(p=runif(10,0,1), n=rep(1:5))
x <- apply(mat, 1, function(z) rbinom(1, z['n'], z['p']))
mat <- cbind(mat, x=x)
I have a column of probabilities and sample sizes, I would like to create a
column of binomial random variables using those corresponding probabilities.
Eg.
mat = as.matrix(cbind(p=runif(10,0,1), n=rep(1:5)))
p n
[1,] 0.5093493 1
[2,] 0.4947375 2
[3,] 0.6753015 3
[4,] 0.8595729 4
[5,] 0.1004739 5
[6,] 0.6292883 1
[7,] 0.3752004 2
[8,] 0.6889157 3
[9,] 0.2435880 4
[10,] 0.9619128 5
I want to create mat$x as binomial(n, p)
Thanks,
Robin
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Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
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