[−][src]Trait rand::seq::SliceRandom

pub trait SliceRandom {
    type Item;
    fn choose<R: ?Sized>(&self, rng: &mut R) -> Option<&Self::Item>
    where
        R: Rng;

    fn choose_mut<R: ?Sized>(&mut self, rng: &mut R) -> Option<&mut Self::Item>
    where
        R: Rng;

    fn choose_multiple<R: ?Sized>(
        &self, 
        rng: &mut R, 
        amount: usize
    ) -> SliceChooseIter<Self, Self::Item>
    where
        R: Rng;

    fn choose_weighted<R: ?Sized, F, B, X>(
        &self, 
        rng: &mut R, 
        weight: F
    ) -> Result<&Self::Item, WeightedError>
    where
        R: Rng,
        F: Fn(&Self::Item) -> B,
        B: SampleBorrow<X>,
        X: SampleUniform + for<'a> AddAssign<&'a X> + PartialOrd<X> + Clone + Default;

    fn choose_weighted_mut<R: ?Sized, F, B, X>(
        &mut self, 
        rng: &mut R, 
        weight: F
    ) -> Result<&mut Self::Item, WeightedError>
    where
        R: Rng,
        F: Fn(&Self::Item) -> B,
        B: SampleBorrow<X>,
        X: SampleUniform + for<'a> AddAssign<&'a X> + PartialOrd<X> + Clone + Default;

    fn shuffle<R: ?Sized>(&mut self, rng: &mut R)
    where
        R: Rng;

    fn partial_shuffle<R: ?Sized>(
        &mut self, 
        rng: &mut R, 
        amount: usize
    ) -> (&mut [Self::Item], &mut [Self::Item])
    where
        R: Rng;
}

Extension trait on slices, providing random mutation and sampling methods.

An implementation is provided for slices. This may also be implementable for other types.

Associated Types

type Item

The element type.

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Required methods

fn choose<R: ?Sized>(&self, rng: &mut R) -> Option<&Self::Item> where
    R: Rng, 

Returns a reference to one random element of the slice, or None if the slice is empty.

Depending on the implementation, complexity is expected to be O(1).

Example

use rand::thread_rng;
use rand::seq::SliceRandom;

let choices = [1, 2, 4, 8, 16, 32];
let mut rng = thread_rng();
println!("{:?}", choices.choose(&mut rng));
assert_eq!(choices[..0].choose(&mut rng), None);

fn choose_mut<R: ?Sized>(&mut self, rng: &mut R) -> Option<&mut Self::Item> where
    R: Rng, 

Returns a mutable reference to one random element of the slice, or None if the slice is empty.

Depending on the implementation, complexity is expected to be O(1).

ⓘImportant traits for SliceChooseIter<'a, S, T>
fn choose_multiple<R: ?Sized>(
    &self,
    rng: &mut R,
    amount: usize
) -> SliceChooseIter<Self, Self::Item> where
    R: Rng, 

Produces an iterator that chooses amount elements from the slice at random without repeating any, and returns them in random order.

In case this API is not sufficiently flexible, use index::sample then apply the indices to the slice.

Complexity is expected to be the same as index::sample.

Example

use rand::seq::SliceRandom;
 
let mut rng = &mut rand::thread_rng();
let sample = "Hello, audience!".as_bytes();
 
// collect the results into a vector:
let v: Vec<u8> = sample.choose_multiple(&mut rng, 3).cloned().collect();
 
// store in a buffer:
let mut buf = [0u8; 5];
for (b, slot) in sample.choose_multiple(&mut rng, buf.len()).zip(buf.iter_mut()) {
    *slot = *b;
}

fn choose_weighted<R: ?Sized, F, B, X>(
    &self,
    rng: &mut R,
    weight: F
) -> Result<&Self::Item, WeightedError> where
    R: Rng,
    F: Fn(&Self::Item) -> B,
    B: SampleBorrow<X>,
    X: SampleUniform + for<'a> AddAssign<&'a X> + PartialOrd<X> + Clone + Default, 

Similar to choose, where the likelihood of each outcome may be specified. The specified function weight maps items x to a relative likelihood weight(x). The probability of each item being selected is therefore weight(x) / s, where s is the sum of all weight(x).

Example

use rand::prelude::*;

let choices = [('a', 2), ('b', 1), ('c', 1)];
let mut rng = thread_rng();
// 50% chance to print 'a', 25% chance to print 'b', 25% chance to print 'c'
println!("{:?}", choices.choose_weighted(&mut rng, |item| item.1).unwrap().0);

fn choose_weighted_mut<R: ?Sized, F, B, X>(
    &mut self,
    rng: &mut R,
    weight: F
) -> Result<&mut Self::Item, WeightedError> where
    R: Rng,
    F: Fn(&Self::Item) -> B,
    B: SampleBorrow<X>,
    X: SampleUniform + for<'a> AddAssign<&'a X> + PartialOrd<X> + Clone + Default, 

Similar to choose_mut, where the likelihood of each outcome may be specified. The specified function weight maps items x to a relative likelihood weight(x). The probability of each item being selected is therefore weight(x) / s, where s is the sum of all weight(x).

See also choose_weighted.

fn shuffle<R: ?Sized>(&mut self, rng: &mut R) where
    R: Rng, 

Shuffle a mutable slice in place.

Depending on the implementation, complexity is expected to be O(1).

Example

use rand::thread_rng;
use rand::seq::SliceRandom;

let mut rng = thread_rng();
let mut y = [1, 2, 3, 4, 5];
println!("Unshuffled: {:?}", y);
y.shuffle(&mut rng);
println!("Shuffled:   {:?}", y);

fn partial_shuffle<R: ?Sized>(
    &mut self,
    rng: &mut R,
    amount: usize
) -> (&mut [Self::Item], &mut [Self::Item]) where
    R: Rng, 

Shuffle a slice in place, but exit early.

Returns two mutable slices from the source slice. The first contains amount elements randomly permuted. The second has the remaining elements that are not fully shuffled.

This is an efficient method to select amount elements at random from the slice, provided the slice may be mutated.

If you only need to choose elements randomly and amount > self.len()/2 then you may improve performance by taking amount = values.len() - amount and using only the second slice.

If amount is greater than the number of elements in the slice, this will perform a full shuffle.

Complexity is expected to be O(m) where m = amount.

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Implementations on Foreign Types

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

type Item = T

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Implementors

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