Struct rand::distributions::weighted::WeightedIndex
source · [−]pub struct WeightedIndex<X: SampleUniform + PartialOrd> { /* private fields */ }
Expand description
A distribution using weighted sampling of discrete items
Sampling a WeightedIndex
distribution returns the index of a randomly
selected element from the iterator used when the WeightedIndex
was
created. The chance of a given element being picked is proportional to the
value of the element. The weights can use any type X
for which an
implementation of Uniform<X>
exists.
Performance
Time complexity of sampling from WeightedIndex
is O(log N)
where
N
is the number of weights. As an alternative,
rand_distr::weighted_alias
supports O(1)
sampling, but with much higher initialisation cost.
A WeightedIndex<X>
contains a Vec<X>
and a Uniform<X>
and so its
size is the sum of the size of those objects, possibly plus some alignment.
Creating a WeightedIndex<X>
will allocate enough space to hold N - 1
weights of type X
, where N
is the number of weights. However, since
Vec
doesn’t guarantee a particular growth strategy, additional memory
might be allocated but not used. Since the WeightedIndex
object also
contains, this might cause additional allocations, though for primitive
types, Uniform<X>
doesn’t allocate any memory.
Sampling from WeightedIndex
will result in a single call to
Uniform<X>::sample
(method of the Distribution
trait), which typically
will request a single value from the underlying RngCore
, though the
exact number depends on the implementation of Uniform<X>::sample
.
Example
use rand::prelude::*;
use rand::distributions::WeightedIndex;
let choices = ['a', 'b', 'c'];
let weights = [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)).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
sourceimpl<X: SampleUniform + PartialOrd> WeightedIndex<X>
impl<X: SampleUniform + PartialOrd> WeightedIndex<X>
sourcepub fn new<I>(weights: I) -> Result<WeightedIndex<X>, WeightedError> where
I: IntoIterator,
I::Item: SampleBorrow<X>,
X: for<'a> AddAssign<&'a X> + Clone + Default,
pub fn new<I>(weights: I) -> Result<WeightedIndex<X>, WeightedError> where
I: IntoIterator,
I::Item: SampleBorrow<X>,
X: for<'a> AddAssign<&'a X> + Clone + Default,
Creates a new a WeightedIndex
Distribution
using the values
in weights
. The weights can use any type X
for which an
implementation of Uniform<X>
exists.
Returns an error if the iterator is empty, if any weight is < 0
, or
if its total value is 0.
sourcepub fn update_weights(
&mut self,
new_weights: &[(usize, &X)]
) -> Result<(), WeightedError> where
X: for<'a> AddAssign<&'a X> + for<'a> SubAssign<&'a X> + Clone + Default,
pub fn update_weights(
&mut self,
new_weights: &[(usize, &X)]
) -> Result<(), WeightedError> where
X: for<'a> AddAssign<&'a X> + for<'a> SubAssign<&'a X> + Clone + Default,
Update a subset of weights, without changing the number of weights.
new_weights
must be sorted by the index.
Using this method instead of new
might be more efficient if only a small number of
weights is modified. No allocations are performed, unless the weight type X
uses
allocation internally.
In case of error, self
is not modified.
Trait Implementations
sourceimpl<X: Clone + SampleUniform + PartialOrd> Clone for WeightedIndex<X> where
X::Sampler: Clone,
impl<X: Clone + SampleUniform + PartialOrd> Clone for WeightedIndex<X> where
X::Sampler: Clone,
sourcefn clone(&self) -> WeightedIndex<X>
fn clone(&self) -> WeightedIndex<X>
Returns a copy of the value. Read more
1.0.0 · sourcefn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
sourceimpl<X: Debug + SampleUniform + PartialOrd> Debug for WeightedIndex<X> where
X::Sampler: Debug,
impl<X: Debug + SampleUniform + PartialOrd> Debug for WeightedIndex<X> where
X::Sampler: Debug,
sourceimpl<X> Distribution<usize> for WeightedIndex<X> where
X: SampleUniform + PartialOrd,
impl<X> Distribution<usize> for WeightedIndex<X> where
X: SampleUniform + PartialOrd,
sourcefn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> usize
fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> usize
Generate a random value of T
, using rng
as the source of randomness.
sourcefn sample_iter<R>(self, rng: R) -> DistIter<Self, R, T>ⓘNotable traits for DistIter<D, R, T>impl<D, R, T> Iterator for DistIter<D, R, T> where
D: Distribution<T>,
R: Rng, type Item = T;
where
R: Rng,
Self: Sized,
fn sample_iter<R>(self, rng: R) -> DistIter<Self, R, T>ⓘNotable traits for DistIter<D, R, T>impl<D, R, T> Iterator for DistIter<D, R, T> where
D: Distribution<T>,
R: Rng, type Item = T;
where
R: Rng,
Self: Sized,
D: Distribution<T>,
R: Rng, type Item = T;
Create an iterator that generates random values of T
, using rng
as
the source of randomness. Read more
sourceimpl<X: PartialEq + SampleUniform + PartialOrd> PartialEq<WeightedIndex<X>> for WeightedIndex<X> where
X::Sampler: PartialEq,
impl<X: PartialEq + SampleUniform + PartialOrd> PartialEq<WeightedIndex<X>> for WeightedIndex<X> where
X::Sampler: PartialEq,
sourcefn eq(&self, other: &WeightedIndex<X>) -> bool
fn eq(&self, other: &WeightedIndex<X>) -> bool
This method tests for self
and other
values to be equal, and is used
by ==
. Read more
sourcefn ne(&self, other: &WeightedIndex<X>) -> bool
fn ne(&self, other: &WeightedIndex<X>) -> bool
This method tests for !=
.
impl<X: SampleUniform + PartialOrd> StructuralPartialEq for WeightedIndex<X>
Auto Trait Implementations
impl<X> RefUnwindSafe for WeightedIndex<X> where
X: RefUnwindSafe,
<X as SampleUniform>::Sampler: RefUnwindSafe,
impl<X> Send for WeightedIndex<X> where
X: Send,
<X as SampleUniform>::Sampler: Send,
impl<X> Sync for WeightedIndex<X> where
X: Sync,
<X as SampleUniform>::Sampler: Sync,
impl<X> Unpin for WeightedIndex<X> where
X: Unpin,
<X as SampleUniform>::Sampler: Unpin,
impl<X> UnwindSafe for WeightedIndex<X> where
X: UnwindSafe,
<X as SampleUniform>::Sampler: UnwindSafe,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<T> ToOwned for T where
T: Clone,
impl<T> ToOwned for T where
T: Clone,
type Owned = T
type Owned = T
The resulting type after obtaining ownership.
sourcefn clone_into(&self, target: &mut T)
fn clone_into(&self, target: &mut T)
toowned_clone_into
)Uses borrowed data to replace owned data, usually by cloning. Read more