Generating data from a uniform distribution using R, without using R's runif function

Generating data from a uniform distribution using R, without using the runif function

Shravan Vasishth

12/19/2021

One can easily generate data from a uniform(0,1) using the runif function in R:

runif(10)

##  [1] 0.25873184 0.06723362 0.07725857 0.65281945 0.43817895 0.35372059
##  [7] 0.14399150 0.16840633 0.24538047 0.95230596

But what if one doesn’t have this function and one needs to generate samples from a uniform(0,1)? In rejection sampling, one needs access to uniform(0,1) .

Here is one way to generate uniform data.

Generating samples from a uniform(0,1)

Samples from a uniform can be generated using the linear congruent generator algorithm (https://en.wikipedia.org/wiki/Linear_congruential_generator).

Here is the code in R.

pseudo_unif<-function(mult=16807,
                      mod=(2^31)-1,
                      seed=123456789,
                      size=100000){
  U<-rep(NA,size)
  x<-(seed*mult+1)%%mod
  U[1]<-x/mod
  for(i in 2:size){
    x<-(x*mult+1)%%mod
    U[i]<-x/mod
  }
  return(U)
}

u<-pseudo_unif()
hist(u,freq=FALSE)

For generating data from any range going from min to max:

gen_unif<-function(low=0,high=100,seed=987654321,
                   size=10000){
  low + (high-low)*pseudo_unif(seed=seed,size=size)
}

hist(gen_unif(),freq=FALSE)

The above code is based on: https://towardsdatascience.com/how-to-generate-random-variables-from-scratch-no-library-used-4b71eb3c8dc7