Iteratively draw a sequential Poisson sample

Create a function that draws new units, one at a time, according to the sequential Poisson method without replacing previously sampled units.

Usage

sps_iterator(x, n = 0L, prn = NULL, alpha = 0.001, cutoff = Inf)

Arguments

x

A positive and finite numeric vector of sizes for units in the population (e.g., revenue for drawing a sample of businesses).

n

A positive integer giving the initial sample size for the iterator.

prn

A numeric vector of permanent random numbers for units in the population, distributed uniform between 0 and 1. The default does not use permanent random numbers, instead generating a random vector when the function is called.

alpha

A number between 0 and 1. Units with inclusion probabilities greater than or equal to 1 - alpha are set to 1. The default is slightly larger than 0.

cutoff

A numeric cutoff. Units with x >= cutoff get an inclusion probability of 1. The default does not apply a cutoff.

Value

A function that returns the next unit in the sample. It take a single argument giving the sentinel value to indicate that there are no units left to sample (default NULL).

Examples

prn <- runif(5)
s <- sps_iterator(1:5, prn = prn)
s()
#> [1] 5
s()
#> [1] 2
s()
#> [1] 3

# Same as drawing the sample with 3 units.
sps(1:5, 3, prn = prn)
#> [1] 2 3 5