To interleave or interlace two vectors

I want to interleave two vectors of the same pattern and equal length Say:

a <- rpois(lambda=3,n=5e5)
b <- rpois(lambda=4,n=5e5)

I want to interleave or interleave these two vectors to create an equivalent C (a [1], B [1], a [2], B [2],..., a [length], B [length)])

My first attempt was this:

sapply(X=rep.int(c(3,4),times=5e5),FUN=rpois,n=1)

But it takes rpois to be called more times than needed

So far, my best attempt is to convert it into a matrix and re convert it into a vector:

d <- c(rbind(rpois(lambda=3,n=5e5),rpois(lambda=4,n=5e5)))
d <- c(rbind(a,b))

Is there a better way to do it? Or is there a function in base R to do the same thing?

Solution

Your rbind method should be very good You can also use

rpois(lambda=c(3,n=1e6)

Because r will automatically copy the vector of lambda value to the required length There is not much difference in speed:

library(rbenchmark)
benchmark(rpois(1e6,c(3,4)),c(rbind(rpois(5e5,3),rpois(5e5,4))))


#                                        test replications elapsed relative
# 2 c(rbind(rpois(5e+05,rpois(5e+05,4)))          100  23.390 1.112168
# 1                      rpois(1e+06,4))          100  21.031 1.000000

Elegance is in the eyes of onlookers... Of course, the C (rbind (...)) method is generally used to build alternating vectors, while another solution is specific to rpois or other functions, like copying their parameters