sample(x, size, replace=false)
sample takes a sample of the specified size from
the elements of x using either with or without replacement
sampling according to the value of replace.
By default size is equal to length(x)
so that sample(x) generates a random permutation
of the elements of x.
If x has length 1, sampling takes place from
1:x.
Examples
# a random permutation
sample(x)
# bootstrap sampling
sample(x,replace=true)
# 100 Bernoulli trials
sample(c(0,1), 100)