# Struct rand_distr::weighted_alias::WeightedAliasIndex

``pub struct WeightedAliasIndex<W: AliasableWeight> { /* private fields */ }``
Expand description

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

Sampling a `WeightedAliasIndex<W>` distribution returns the index of a randomly selected element from the vector used to create the `WeightedAliasIndex<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 `AliasableWeight` exists.

## §Performance

Given that `n` is the number of items in the vector used to create an `WeightedAliasIndex<W>`, it 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 `WeightedAliasIndex<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_distr::WeightedAliasIndex;
use rand::prelude::*;

let choices = vec!['a', 'b', 'c'];
let weights = vec![2, 1, 1];
let dist = WeightedAliasIndex::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 = WeightedAliasIndex::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§

source§

### impl<W: AliasableWeight> WeightedAliasIndex<W>

source

#### pub fn new(weights: Vec<W>) -> Result<Self, WeightError>

Creates a new `WeightedAliasIndex`.

Error cases:

## Trait Implementations§

source§

### impl<W: AliasableWeight> Clone for WeightedAliasIndex<W>where Uniform<W>: Clone,

source§

#### fn clone(&self) -> Self

Returns a copy of the value. Read more
1.0.0 · source§

#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
source§

### impl<W> Debug for WeightedAliasIndex<W>where W: Debug + AliasableWeight, Uniform<W>: Debug,

source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
source§

### impl<'de, W> Deserialize<'de> for WeightedAliasIndex<W>where W: Deserialize<'de> + AliasableWeight, W::Sampler: Deserialize<'de>,

source§

#### fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more
source§

### impl<W: AliasableWeight> Distribution<usize> for WeightedAliasIndex<W>

source§

#### fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> usize

Generate a random value of `T`, using `rng` as the source of randomness.
source§

#### fn sample_iter<R>(self, rng: R) -> DistIter<Self, R, T> ⓘwhere R: Rng, Self: Sized,

Create an iterator that generates random values of `T`, using `rng` as the source of randomness. Read more
source§

#### fn map<F, S>(self, func: F) -> DistMap<Self, F, T, S>where F: Fn(T) -> S, Self: Sized,

Create a distribution of values of ‘S’ by mapping the output of `Self` through the closure `F` Read more
source§

### impl<W> Serialize for WeightedAliasIndex<W>where W: Serialize + AliasableWeight, W::Sampler: Serialize,

source§

#### fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>where __S: Serializer,

Serialize this value into the given Serde serializer. Read more

§

§

§

§

§

§

## Blanket Implementations§

source§

### impl<T> Any for Twhere T: 'static + ?Sized,

source§

#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
source§

### impl<T> Borrow<T> for Twhere T: ?Sized,

source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

### impl<T> BorrowMut<T> for Twhere T: ?Sized,

source§

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

### impl<T> CloneToUninit for Twhere T: Clone,

source§

#### unsafe fn clone_to_uninit(&self, dst: *mut T)

🔬This is a nightly-only experimental API. (`clone_to_uninit`)
Performs copy-assignment from `self` to `dst`. Read more
source§

### impl<T> From<T> for T

source§

#### fn from(t: T) -> T

Returns the argument unchanged.

source§

### impl<T, U> Into<U> for Twhere U: From<T>,

source§

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

source§

### impl<T> ToOwned for Twhere T: Clone,

source§

#### type Owned = T

The resulting type after obtaining ownership.
source§

#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
source§

#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
source§

### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

source§

#### type Error = Infallible

The type returned in the event of a conversion error.
source§

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

source§

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

The type returned in the event of a conversion error.
source§

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
source§

source§

source§