Problem Statement

A method of choosing a line randomly from a file: Is to:

Note: You may choose a smaller number of repetitions if necessary, but mention this up-front. Note: This is a specific version of a Reservoir Sampling algorithm: https://en.wikipedia.org/wiki/Reservoir_sampling

Let's start with the solution:

one_of_n <- function(n)
{
  choice <- 1L
  
  for (i in 2:n)
  {
    if (i*runif(1) < 1)
      choice <- i
  }
  
  return(choice)
}

table(sapply(1:1000000, function(i) one_of_n(10)))