[][src]Struct rand::distributions::weighted::alias_method::WeightedIndex

pub struct WeightedIndex<W: Weight> { /* fields omitted */ }

A distribution using weighted sampling to pick a discretely selected item.

Sampling a WeightedIndex<W> distribution returns the index of a randomly selected element from the vector used to create the WeightedIndex<W>. The chance of a given element being picked is proportional to the value of the element. The weights can have any type W for which a implementation of Weight exists.

Performance

Given that n is the number of items in the vector used to create an WeightedIndex<W>, WeightedIndex<W> will require O(n) amount of memory. More specifically it takes up some constant amount of memory plus the vector used to create it and a Vec<u32> with capacity n.

Time complexity for the creation of a WeightedIndex<W> is O(n). Sampling is O(1), it makes a call to Uniform<u32>::sample and a call to Uniform<W>::sample.

Example

use rand::distributions::weighted::alias_method::WeightedIndex;
use rand::prelude::*;

let choices = vec!['a', 'b', 'c'];
let weights = vec![2, 1, 1];
let dist = WeightedIndex::new(weights).unwrap();
let mut rng = thread_rng();
for _ in 0..100 {
    // 50% chance to print 'a', 25% chance to print 'b', 25% chance to print 'c'
    println!("{}", choices[dist.sample(&mut rng)]);
}

let items = [('a', 0), ('b', 3), ('c', 7)];
let dist2 = WeightedIndex::new(items.iter().map(|item| item.1).collect()).unwrap();
for _ in 0..100 {
    // 0% chance to print 'a', 30% chance to print 'b', 70% chance to print 'c'
    println!("{}", items[dist2.sample(&mut rng)].0);
}

Implementations

impl<W: Weight> WeightedIndex<W>[src]

pub fn new(weights: Vec<W>) -> Result<Self, WeightedError>[src]

Creates a new WeightedIndex.

Returns an error if:

  • The vector is empty.
  • The vector is longer than u32::MAX.
  • For any weight w: w < 0 or w > max where max = W::MAX / weights.len().
  • The sum of weights is zero.

Trait Implementations

impl<W: Weight> Clone for WeightedIndex<W> where
    Uniform<W>: Clone
[src]

impl<W: Weight> Debug for WeightedIndex<W> where
    W: Debug,
    Uniform<W>: Debug
[src]

impl<W: Weight> Distribution<usize> for WeightedIndex<W>[src]

Auto Trait Implementations

impl<W> RefUnwindSafe for WeightedIndex<W> where
    W: RefUnwindSafe,
    <W as SampleUniform>::Sampler: RefUnwindSafe

impl<W> Send for WeightedIndex<W> where
    W: Send,
    <W as SampleUniform>::Sampler: Send

impl<W> Sync for WeightedIndex<W> where
    W: Sync,
    <W as SampleUniform>::Sampler: Sync

impl<W> Unpin for WeightedIndex<W> where
    W: Unpin,
    <W as SampleUniform>::Sampler: Unpin

impl<W> UnwindSafe for WeightedIndex<W> where
    W: UnwindSafe,
    <W as SampleUniform>::Sampler: UnwindSafe

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

impl<T> From<T> for T[src]

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

The resulting type after obtaining ownership.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

impl<V, T> VZip<V> for T where
    V: MultiLane<T>, 
[src]