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use rand::distributions::{Distribution, Uniform};
use crate::{
set::traits::Finite,
traits::{Collecting, ToIterator},
};
pub mod trait_impl;
pub trait Sample<'a, I: Iterator<Item = E>, E, O: Collecting<E> + Default>:
Finite + ToIterator<'a, I, E> {
fn sample_subset_without_replacement<'s: 'a>(
&'s self,
size: usize,
) -> Result<O, String> {
let mut remaining = self.size();
if size > remaining {
return Err(format!(
"desired sample size {} > population size {}",
size, remaining
));
}
let mut samples = O::default();
let mut needed = size;
let mut rng = rand::thread_rng();
let uniform = Uniform::new(0., 1.);
for element in self.to_iter() {
if uniform.sample(&mut rng) <= (needed as f64 / remaining as f64) {
samples.collect(element);
needed -= 1;
}
remaining -= 1;
}
Ok(samples)
}
fn sample_with_replacement<'s: 'a>(
&'s self,
size: usize,
) -> Result<O, String> {
let population_size = self.size();
if population_size == 0 {
return Err(
"cannot sample from a population of 0 elements".to_string()
);
}
let mut samples = O::default();
let mut rng = rand::thread_rng();
let uniform = Uniform::new(0., population_size as f64);
for _ in 0..size {
samples.collect(
self.to_iter()
.nth(uniform.sample(&mut rng) as usize)
.unwrap(),
);
}
Ok(samples)
}
}
#[cfg(test)]
mod tests {
use crate::set::{
contiguous_integer_set::ContiguousIntegerSet,
ordered_integer_set::OrderedIntegerSet, traits::Finite,
};
use super::Sample;
#[test]
fn test_sampling_without_replacement() {
let interval = ContiguousIntegerSet::new(0, 100);
let num_samples = 25;
let samples = interval
.sample_subset_without_replacement(num_samples)
.unwrap();
assert_eq!(samples.size(), num_samples);
let set =
OrderedIntegerSet::from_slice(&[[-89, -23], [-2, 100], [300, 345]]);
let num_samples = 18;
let samples =
set.sample_subset_without_replacement(num_samples).unwrap();
assert_eq!(samples.size(), num_samples);
}
#[test]
fn test_sampling_with_replacement() {
let num_samples = 25;
let v = vec![1];
let samples = v.sample_with_replacement(num_samples);
assert_eq!(samples, Ok(vec![1; num_samples]));
assert!(Vec::<f32>::new()
.sample_with_replacement(num_samples)
.is_err());
}
}