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| </pre><pre class="rust"><code><span class="comment">// Copyright 2021 Developers of the Rand project. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // https://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::distributions::{Distribution, Uniform}; |
| |
| <span class="doccomment">/// A distribution to sample items uniformly from a slice. |
| /// |
| /// [`Slice::new`] constructs a distribution referencing a slice and uniformly |
| /// samples references from the items in the slice. It may do extra work up |
| /// front to make sampling of multiple values faster; if only one sample from |
| /// the slice is required, [`SliceRandom::choose`] can be more efficient. |
| /// |
| /// Steps are taken to avoid bias which might be present in naive |
| /// implementations; for example `slice[rng.gen() % slice.len()]` samples from |
| /// the slice, but may be more likely to select numbers in the low range than |
| /// other values. |
| /// |
| /// This distribution samples with replacement; each sample is independent. |
| /// Sampling without replacement requires state to be retained, and therefore |
| /// cannot be handled by a distribution; you should instead consider methods |
| /// on [`SliceRandom`], such as [`SliceRandom::choose_multiple`]. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use rand::Rng; |
| /// use rand::distributions::Slice; |
| /// |
| /// let vowels = ['a', 'e', 'i', 'o', 'u']; |
| /// let vowels_dist = Slice::new(&vowels).unwrap(); |
| /// let rng = rand::thread_rng(); |
| /// |
| /// // build a string of 10 vowels |
| /// let vowel_string: String = rng |
| /// .sample_iter(&vowels_dist) |
| /// .take(10) |
| /// .collect(); |
| /// |
| /// println!("{}", vowel_string); |
| /// assert_eq!(vowel_string.len(), 10); |
| /// assert!(vowel_string.chars().all(|c| vowels.contains(&c))); |
| /// ``` |
| /// |
| /// For a single sample, [`SliceRandom::choose`][crate::seq::SliceRandom::choose] |
| /// may be preferred: |
| /// |
| /// ``` |
| /// use rand::seq::SliceRandom; |
| /// |
| /// let vowels = ['a', 'e', 'i', 'o', 'u']; |
| /// let mut rng = rand::thread_rng(); |
| /// |
| /// println!("{}", vowels.choose(&mut rng).unwrap()) |
| /// ``` |
| /// |
| /// [`SliceRandom`]: crate::seq::SliceRandom |
| /// [`SliceRandom::choose`]: crate::seq::SliceRandom::choose |
| /// [`SliceRandom::choose_multiple`]: crate::seq::SliceRandom::choose_multiple |
| </span><span class="attribute">#[derive(Debug, Clone, Copy)] |
| </span><span class="kw">pub struct </span>Slice<<span class="lifetime">'a</span>, T> { |
| slice: <span class="kw-2">&</span><span class="lifetime">'a </span>[T], |
| range: Uniform<usize>, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, T> Slice<<span class="lifetime">'a</span>, T> { |
| <span class="doccomment">/// Create a new `Slice` instance which samples uniformly from the slice. |
| /// Returns `Err` if the slice is empty. |
| </span><span class="kw">pub fn </span>new(slice: <span class="kw-2">&</span><span class="lifetime">'a </span>[T]) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>, EmptySlice> { |
| <span class="kw">match </span>slice.len() { |
| <span class="number">0 </span>=> <span class="prelude-val">Err</span>(EmptySlice), |
| len => <span class="prelude-val">Ok</span>(<span class="self">Self </span>{ |
| slice, |
| range: Uniform::new(<span class="number">0</span>, len), |
| }), |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, T> Distribution<<span class="kw-2">&</span><span class="lifetime">'a </span>T> <span class="kw">for </span>Slice<<span class="lifetime">'a</span>, T> { |
| <span class="kw">fn </span>sample<R: <span class="kw">crate</span>::Rng + <span class="question-mark">?</span>Sized>(<span class="kw-2">&</span><span class="self">self</span>, rng: <span class="kw-2">&mut </span>R) -> <span class="kw-2">&</span><span class="lifetime">'a </span>T { |
| <span class="kw">let </span>idx = <span class="self">self</span>.range.sample(rng); |
| |
| <span class="macro">debug_assert!</span>( |
| idx < <span class="self">self</span>.slice.len(), |
| <span class="string">"Uniform::new(0, {}) somehow returned {}"</span>, |
| <span class="self">self</span>.slice.len(), |
| idx |
| ); |
| |
| <span class="comment">// Safety: at construction time, it was ensured that the slice was |
| // non-empty, and that the `Uniform` range produces values in range |
| // for the slice |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.slice.get_unchecked(idx) } |
| } |
| } |
| |
| <span class="doccomment">/// Error type indicating that a [`Slice`] distribution was improperly |
| /// constructed with an empty slice. |
| </span><span class="attribute">#[derive(Debug, Clone, Copy)] |
| </span><span class="kw">pub struct </span>EmptySlice; |
| |
| <span class="kw">impl </span>core::fmt::Display <span class="kw">for </span>EmptySlice { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>core::fmt::Formatter<<span class="lifetime">'_</span>>) -> core::fmt::Result { |
| <span class="macro">write!</span>( |
| f, |
| <span class="string">"Tried to create a `distributions::Slice` with an empty slice" |
| </span>) |
| } |
| } |
| |
| <span class="attribute">#[cfg(feature = <span class="string">"std"</span>)] |
| </span><span class="kw">impl </span>std::error::Error <span class="kw">for </span>EmptySlice {} |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="rand" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
