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use crate::*;
use rand::{rngs::OsRng, RngCore};
use std::hash::Hash;
/// Generator of groups of random items of type `T` with different probabilities.
/// According to the configuration, items in each group can be either
/// repetitive or non-repetitive.
pub struct Picker<T: Clone + Eq + Hash, R: RngCore> {
rng: R,
table: Vec<(T, f64)>,
grid: Vec<f64>,
grid_width: f64,
repetitive: bool,
table_picked: Vec<bool>, // used in `pick_indexes()`, size: table.len()
picked_indexes: Vec<usize>, // read it after calling `pick_indexes()`
}
impl<T: Clone + Eq + Hash> Picker<T, OsRng> {
/// Builds the `Picker` with given configuration, using the OS random source.
pub fn build(conf: Config<T>) -> Result<Self, Error> {
Picker::build_with_rng(conf, OsRng)
}
}
impl<T: Clone + Eq + Hash, R: RngCore> Picker<T, R> {
/// Builds the `Picker` with given configuration and the given random source.
pub fn build_with_rng(conf: Config<T>, rng: R) -> Result<Self, Error> {
let table_len = conf.table.len();
let mut picker = Self {
rng,
table: Vec::with_capacity(table_len),
grid: Vec::with_capacity(table_len),
grid_width: 0.,
repetitive: conf.repetitive,
table_picked: Vec::with_capacity(table_len),
picked_indexes: Vec::with_capacity(table_len),
};
picker.configure(conf)?;
Ok(picker)
}
/// Applies new configuration.
pub fn configure(&mut self, conf: Config<T>) -> Result<(), Error> {
self.table = conf.vec_table()?;
let table_len = self.table.len();
self.grid.clear();
self.grid.reserve(table_len);
let mut cur = 0.;
for (_, val) in &self.table {
cur += val;
self.grid.push(cur);
}
self.grid_width = *self.grid.last().unwrap();
self.repetitive = conf.repetitive;
self.table_picked.resize(table_len, false);
self.picked_indexes.reserve(table_len);
Ok(())
}
/// Returns the size of the weight table that contains all possible choices (p > 0).
///
/// ```
/// use random_picker::Picker;
/// let mut conf: random_picker::Config<String> = "
/// a = 0; b = 1; c = 1.1
/// ".parse().unwrap();
/// let picker = Picker::build(conf.clone()).unwrap();
/// assert_eq!(picker.table_len(), 2);
/// conf.append_str("b = 0; c = 0");
/// assert!(Picker::build(conf).is_err());
/// ```
#[inline(always)]
pub fn table_len(&self) -> usize {
self.table.len()
}
/// Picks `amount` of items and returns the group of items.
/// `amount` must not exceed `table_len()`.
#[inline(always)]
pub fn pick(&mut self, amount: usize) -> Result<Vec<T>, Error> {
self.pick_indexes(amount)?;
Ok(self
.picked_indexes
.iter()
.map(|&i| self.item_key(i))
.collect())
}
/// Picks `dest.len()` of items and writes them into `dest` (avoids allocation).
/// Length of `dest` must not exceed `table_len()`.
#[inline]
pub fn write_to(&mut self, dest: &mut [T]) -> Result<(), Error> {
self.pick_indexes(dest.len())?;
for (i, k) in dest.iter_mut().enumerate() {
*k = self.item_key(self.picked_indexes[i]);
}
Ok(())
}
/// Evaluates probabilities of existences of table items in each group
/// of length `amount`, by generating groups of items for `test_times`.
///
/// ```
/// use random_picker::*;
/// let mut conf: Config<String> = "
/// a=856; b=139; c=297; d=378; e=1304;
/// f=289; g=199; h=528; i=627; j= 13;
/// k= 42; l=339; m=249; n=707; o= 797;
/// p=199; q= 12; r=677; s=607; t=1045;
/// u=249; v= 92; w=149; x= 17; y= 199; z=8;
/// ".parse().unwrap();
/// assert_eq!(conf.repetitive, false);
/// assert_eq!(conf.table.len(), 26);
/// let table_probs = conf.calc_probabilities(3).unwrap();
///
/// let mut picker = Picker::build(conf.clone()).unwrap();
/// let table_freqs = picker.test_freqs(3, 1_000_000).unwrap();
/// for (k, v) in table_freqs.iter() {
/// assert!((*v - *table_probs.get(k).unwrap()).abs() < 0.005);
/// }
///
/// conf.append_str("repetitive = true");
/// assert_eq!(conf.repetitive, true);
/// let table_probs = conf.calc_probabilities(3).unwrap();;
///
/// let mut picker = Picker::build_with_rng(conf, rand::thread_rng()).unwrap();
/// let table_freqs = picker.test_freqs(3, 1_000_000).unwrap();
/// for (k, v) in table_freqs.iter() {
/// assert!((*v - *table_probs.get(k).unwrap()).abs() < 0.005);
/// }
/// ```
pub fn test_freqs(&mut self, amount: usize, test_times: usize) -> Result<Table<T>, Error> {
if test_times == 0 {
return Ok(self.table.iter().map(|(k, _)| (k.clone(), 0.)).collect());
}
let mut tbl_freq = vec![0_usize; self.table_len()];
if !self.repetitive {
for _ in 0..test_times {
self.pick_indexes(amount)?;
for &idx in &self.picked_indexes {
tbl_freq[idx] += 1;
}
}
} else {
let mut tbl_picked = vec![false; self.table_len()];
for _ in 0..test_times {
tbl_picked.fill(false);
self.pick_indexes(amount)?;
for &idx in &self.picked_indexes {
if !tbl_picked[idx] {
tbl_freq[idx] += 1;
tbl_picked[idx] = true;
}
}
}
}
let test_times = test_times as f64;
let table = tbl_freq
.iter()
.enumerate()
.map(|(i, &v)| (self.item_key(i), v as f64 / test_times))
.collect();
Ok(table)
}
/// Picks `amount` of indexes and replaces values in `self.picked_indexes`.
#[inline]
fn pick_indexes(&mut self, amount: usize) -> Result<(), Error> {
if !self.repetitive && amount > self.table_len() {
return Err(Error::InvalidAmount);
}
self.picked_indexes.clear();
self.table_picked.fill(false);
while self.picked_indexes.len() < amount {
let i = self.pick_index()?;
if !self.repetitive {
if self.table_picked[i] {
continue;
}
self.table_picked[i] = true;
}
self.picked_indexes.push(i);
}
Ok(())
}
#[inline(always)]
fn pick_index(&mut self) -> Result<usize, Error> {
let mut bytes = [0u8; 4];
self.rng
.try_fill_bytes(&mut bytes)
.map_err(Error::RandError)?;
let val = (u32::from_ne_bytes(bytes) as f64) / (u32::MAX as f64) * self.grid_width;
for (i, &v) in self.grid.iter().enumerate() {
if val <= v {
return Ok(i);
};
}
Ok(self.table_len() - 1) // almost impossible
}
#[inline(always)]
fn item_key(&self, i: usize) -> T {
self.table[i].0.clone()
}
}