Generate random binary vector with equal Ones and Zeros

Question

In R programming language, say you want to create a random binary vector with 4 elements.

The constraint is that the numbers of one's and zero's have to be equal.

So

(0,0,1,1)
(0,1,1,0)
(1,1,0,0)
...

Is there an easy way to do this?

Answer 1

Just randomly select every case without replacement from a set containing 2 0's and 2 1's.

sample(rep(0:1,each=2))
#[1] 0 1 1 0

Always works:

replicate(3,sample(rep(0:1,each=2)),simplify=FALSE)
#[[1]]
#[1] 1 0 0 1
#
#[[2]]
#[1] 0 1 0 1
#
#[[3]]
#[1] 1 1 0 0