Draw random samples from a categorical distribution given a matrix of probabilities.
rcat is vectorized and written in C++ for speed.
rcat(n, prob)Number of random observations to draw.
A matrix of probabilities where rows correspond to observations and columns correspond to categories.
A vector of random samples from the categorical distribution. The length of the sample is determined by n. The numerical arguments other than n are recycled so that the number of samples is equal to n.
p <- c(.2, .5, .3)
n <- 10000
pmat <- matrix(rep(p, n), nrow = n, ncol = length(p), byrow = TRUE)
# rcat
set.seed(100)
ptm <- proc.time()
samp1 <- rcat(n, pmat)
proc.time() - ptm
#> user system elapsed
#> 0.003 0.000 0.003
prop.table(table(samp1))
#> samp1
#> 1 2 3
#> 0.2015 0.5089 0.2896
# rmultinom from base R
set.seed(100)
ptm <- proc.time()
samp2 <- t(apply(pmat, 1, rmultinom, n = 1, size = 1))
samp2 <- apply(samp2, 1, function(x) which(x == 1))
proc.time() - ptm
#> user system elapsed
#> 0.067 0.000 0.067
prop.table(table(samp2))
#> samp2
#> 1 2 3
#> 0.2015 0.5089 0.2896