Struct rand_distr::weighted_alias::WeightedAliasIndex [−][src]
pub struct WeightedAliasIndex<W: AliasableWeight> { /* fields omitted */ }
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
Creates a new WeightedAliasIndex
.
Returns an error if:
- The vector is empty.
- The vector is longer than
u32::MAX
. - For any weight
w
:w < 0
orw > max
wheremax = W::MAX / weights.len()
. - The sum of weights is zero.
Trait Implementations
Generate a random value of T
, using rng
as the source of randomness.
Create an iterator that generates random values of T
, using rng
as
the source of randomness. Read more
Auto Trait Implementations
impl<W> RefUnwindSafe for WeightedAliasIndex<W> where
W: RefUnwindSafe,
<W as SampleUniform>::Sampler: RefUnwindSafe,
impl<W> Send for WeightedAliasIndex<W> where
W: Send,
<W as SampleUniform>::Sampler: Send,
impl<W> Sync for WeightedAliasIndex<W> where
W: Sync,
<W as SampleUniform>::Sampler: Sync,
impl<W> Unpin for WeightedAliasIndex<W> where
<W as SampleUniform>::Sampler: Unpin,
impl<W> UnwindSafe for WeightedAliasIndex<W> where
W: UnwindSafe,
<W as SampleUniform>::Sampler: UnwindSafe,
Blanket Implementations
Mutably borrows from an owned value. Read more
pub fn vzip(self) -> V