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153 lines
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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Extension trait on indexable lists, providing random sampling methods."><title>IndexedRandom in rand::seq - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="rand" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../../static.files/storage-e2aeef58.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-263c88ec.css"></noscript><link rel="icon" href="https://www.rust-lang.org/favicon.ico"></head><body class="rustdoc trait"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><rustdoc-topbar><h2><a href="#">IndexedRandom</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../../rand/index.html"><img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></a><h2><a href="../../rand/index.html">rand</a><span class="version">0.9.2</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Indexed<wbr>Random</a></h2><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.len" title="len">len</a></li></ul><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.choose" title="choose">choose</a></li><li><a href="#method.choose_multiple" title="choose_multiple">choose_multiple</a></li><li><a href="#method.choose_multiple_array" title="choose_multiple_array">choose_multiple_array</a></li><li><a href="#method.choose_multiple_weighted" title="choose_multiple_weighted">choose_multiple_weighted</a></li><li><a href="#method.choose_weighted" title="choose_weighted">choose_weighted</a></li><li><a href="#method.is_empty" title="is_empty">is_empty</a></li></ul><h3><a href="#foreign-impls">Implementations on Foreign Types</a></h3><ul class="block"><li><a href="#impl-IndexedRandom-for-%5BT%5D" title="[T]">[T]</a></li></ul><h3><a href="#dyn-compatibility">Dyn Compatibility</a></h3><h3><a href="#implementors">Implementors</a></h3></section><div id="rustdoc-modnav"><h2><a href="index.html">In rand::<wbr>seq</a></h2></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><div class="rustdoc-breadcrumbs"><a href="../index.html">rand</a>::<wbr><a href="index.html">seq</a></div><h1>Trait <span class="trait">Indexed<wbr>Random</span> <button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../../src/rand/seq/slice.rs.html#25-236">Source</a> </span></div><pre class="rust item-decl"><code>pub trait IndexedRandom: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html" title="trait core::ops::index::Index">Index</a><<a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>> {
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// Required method
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fn <a href="#tymethod.len" class="fn">len</a>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>;
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// Provided methods
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fn <a href="#method.is_empty" class="fn">is_empty</a>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.bool.html">bool</a> { ... }
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<span class="item-spacer"></span> fn <a href="#method.choose" class="fn">choose</a><R>(&self, rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>>
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<span class="where">where R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
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<span class="item-spacer"></span> fn <a href="#method.choose_multiple" class="fn">choose_multiple</a><R>(
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&self,
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rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
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amount: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>,
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) -> <a class="struct" href="struct.SliceChooseIter.html" title="struct rand::seq::SliceChooseIter">SliceChooseIter</a><'_, Self, Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>> <a href="#" class="tooltip" data-notable-ty="SliceChooseIter<'_, Self, Self::Output>">ⓘ</a>
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<span class="where">where Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
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<span class="item-spacer"></span> fn <a href="#method.choose_multiple_array" class="fn">choose_multiple_array</a><R, const N: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>>(
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&self,
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rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
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) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><[Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>; <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.array.html">N</a>]>
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<span class="where">where Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/clone/trait.Clone.html" title="trait core::clone::Clone">Clone</a> + <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
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<span class="item-spacer"></span> fn <a href="#method.choose_weighted" class="fn">choose_weighted</a><R, F, B, X>(
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&self,
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rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
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weight: F,
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) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/result/enum.Result.html" title="enum core::result::Result">Result</a><&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>, <a class="enum" href="../distr/weighted/enum.Error.html" title="enum rand::distr::weighted::Error">WeightError</a>>
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<span class="where">where R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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F: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>) -> B,
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B: <a class="trait" href="../distr/uniform/trait.SampleBorrow.html" title="trait rand::distr::uniform::SampleBorrow">SampleBorrow</a><X>,
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X: <a class="trait" href="../distr/uniform/trait.SampleUniform.html" title="trait rand::distr::uniform::SampleUniform">SampleUniform</a> + <a class="trait" href="../distr/weighted/trait.Weight.html" title="trait rand::distr::weighted::Weight">Weight</a> + <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/cmp/trait.PartialOrd.html" title="trait core::cmp::PartialOrd">PartialOrd</a><X></span> { ... }
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<span class="item-spacer"></span> fn <a href="#method.choose_multiple_weighted" class="fn">choose_multiple_weighted</a><R, F, X>(
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&self,
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rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
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amount: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>,
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weight: F,
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) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="struct" href="struct.SliceChooseIter.html" title="struct rand::seq::SliceChooseIter">SliceChooseIter</a><'_, Self, Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>>, <a class="enum" href="../distr/weighted/enum.Error.html" title="enum rand::distr::weighted::Error">WeightError</a>>
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<span class="where">where Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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F: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>) -> X,
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X: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/convert/trait.Into.html" title="trait core::convert::Into">Into</a><<a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.f64.html">f64</a>></span> { ... }
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}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Extension trait on indexable lists, providing random sampling methods.</p>
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<p>This trait is implemented on <code>[T]</code> slice types. Other types supporting
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<a href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html" title="trait core::ops::index::Index"><code>std::ops::Index<usize></code></a> may implement this (only <a href="trait.IndexedRandom.html#tymethod.len"><code>Self::len</code></a> must be
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specified).</p>
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</div></details><h2 id="required-methods" class="section-header">Required Methods<a href="#required-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="tymethod.len" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#27">Source</a><h4 class="code-header">fn <a href="#tymethod.len" class="fn">len</a>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a></h4></section></summary><div class="docblock"><p>The length</p>
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</div></details></div><h2 id="provided-methods" class="section-header">Provided Methods<a href="#provided-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="method.is_empty" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#31-33">Source</a><h4 class="code-header">fn <a href="#method.is_empty" class="fn">is_empty</a>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.bool.html">bool</a></h4></section></summary><div class="docblock"><p>True when the length is zero</p>
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</div></details><details class="toggle method-toggle" open><summary><section id="method.choose" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#52-61">Source</a><h4 class="code-header">fn <a href="#method.choose" class="fn">choose</a><R>(&self, rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>><div class="where">where
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R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Uniformly sample one element</p>
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<p>Returns a reference to one uniformly-sampled random element of
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the slice, or <code>None</code> if the slice is empty.</p>
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<p>For slices, complexity is <code>O(1)</code>.</p>
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<h5 id="example"><a class="doc-anchor" href="#example">§</a>Example</h5>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::seq::IndexedRandom;
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<span class="kw">let </span>choices = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">4</span>, <span class="number">8</span>, <span class="number">16</span>, <span class="number">32</span>];
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<span class="kw">let </span><span class="kw-2">mut </span>rng = rand::rng();
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<span class="macro">println!</span>(<span class="string">"{:?}"</span>, choices.choose(<span class="kw-2">&mut </span>rng));
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<span class="macro">assert_eq!</span>(choices[..<span class="number">0</span>].choose(<span class="kw-2">&mut </span>rng), <span class="prelude-val">None</span>);</code></pre></div></div></details><details class="toggle method-toggle" open><summary><section id="method.choose_multiple" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#90-105">Source</a><h4 class="code-header">fn <a href="#method.choose_multiple" class="fn">choose_multiple</a><R>(
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&self,
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rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
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amount: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>,
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) -> <a class="struct" href="struct.SliceChooseIter.html" title="struct rand::seq::SliceChooseIter">SliceChooseIter</a><'_, Self, Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>> <a href="#" class="tooltip" data-notable-ty="SliceChooseIter<'_, Self, Self::Output>">ⓘ</a><div class="where">where
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Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Uniformly sample <code>amount</code> distinct elements from self</p>
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<p>Chooses <code>amount</code> elements from the slice at random, without repetition,
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and in random order. The returned iterator is appropriate both for
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collection into a <code>Vec</code> and filling an existing buffer (see example).</p>
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<p>In case this API is not sufficiently flexible, use <a href="index/fn.sample.html" title="fn rand::seq::index::sample"><code>index::sample</code></a>.</p>
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<p>For slices, complexity is the same as <a href="index/fn.sample.html" title="fn rand::seq::index::sample"><code>index::sample</code></a>.</p>
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<h5 id="example-1"><a class="doc-anchor" href="#example-1">§</a>Example</h5>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::seq::IndexedRandom;
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<span class="kw">let </span><span class="kw-2">mut </span>rng = <span class="kw-2">&mut </span>rand::rng();
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<span class="kw">let </span>sample = <span class="string">"Hello, audience!"</span>.as_bytes();
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<span class="comment">// collect the results into a vector:
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</span><span class="kw">let </span>v: Vec<u8> = sample.choose_multiple(<span class="kw-2">&mut </span>rng, <span class="number">3</span>).cloned().collect();
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<span class="comment">// store in a buffer:
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</span><span class="kw">let </span><span class="kw-2">mut </span>buf = [<span class="number">0u8</span>; <span class="number">5</span>];
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<span class="kw">for </span>(b, slot) <span class="kw">in </span>sample.choose_multiple(<span class="kw-2">&mut </span>rng, buf.len()).zip(buf.iter_mut()) {
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<span class="kw-2">*</span>slot = <span class="kw-2">*</span>b;
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}</code></pre></div></div></details><details class="toggle method-toggle" open><summary><section id="method.choose_multiple_array" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#123-130">Source</a><h4 class="code-header">fn <a href="#method.choose_multiple_array" class="fn">choose_multiple_array</a><R, const N: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>>(
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&self,
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rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
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) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/option/enum.Option.html" title="enum core::option::Option">Option</a><[Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>; <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.array.html">N</a>]><div class="where">where
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Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/clone/trait.Clone.html" title="trait core::clone::Clone">Clone</a> + <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
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R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Uniformly sample a fixed-size array of distinct elements from self</p>
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<p>Chooses <code>N</code> elements from the slice at random, without repetition,
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and in random order.</p>
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<p>For slices, complexity is the same as <a href="index/fn.sample_array.html" title="fn rand::seq::index::sample_array"><code>index::sample_array</code></a>.</p>
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<h5 id="example-2"><a class="doc-anchor" href="#example-2">§</a>Example</h5>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::seq::IndexedRandom;
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<span class="kw">let </span><span class="kw-2">mut </span>rng = <span class="kw-2">&mut </span>rand::rng();
|
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<span class="kw">let </span>sample = <span class="string">"Hello, audience!"</span>.as_bytes();
|
||
|
||
<span class="kw">let </span>a: [u8; <span class="number">3</span>] = sample.choose_multiple_array(<span class="kw-2">&mut </span>rng).unwrap();</code></pre></div></div></details><details class="toggle method-toggle" open><summary><section id="method.choose_weighted" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#162-176">Source</a><h4 class="code-header">fn <a href="#method.choose_weighted" class="fn">choose_weighted</a><R, F, B, X>(
|
||
&self,
|
||
rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
|
||
weight: F,
|
||
) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/result/enum.Result.html" title="enum core::result::Result">Result</a><&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>, <a class="enum" href="../distr/weighted/enum.Error.html" title="enum rand::distr::weighted::Error">WeightError</a>><div class="where">where
|
||
R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
|
||
F: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>) -> B,
|
||
B: <a class="trait" href="../distr/uniform/trait.SampleBorrow.html" title="trait rand::distr::uniform::SampleBorrow">SampleBorrow</a><X>,
|
||
X: <a class="trait" href="../distr/uniform/trait.SampleUniform.html" title="trait rand::distr::uniform::SampleUniform">SampleUniform</a> + <a class="trait" href="../distr/weighted/trait.Weight.html" title="trait rand::distr::weighted::Weight">Weight</a> + <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/cmp/trait.PartialOrd.html" title="trait core::cmp::PartialOrd">PartialOrd</a><X>,</div></h4></section></summary><div class="docblock"><p>Biased sampling for one element</p>
|
||
<p>Returns a reference to one element of the slice, sampled according
|
||
to the provided weights. Returns <code>None</code> only if the slice is empty.</p>
|
||
<p>The specified function <code>weight</code> maps each item <code>x</code> to a relative
|
||
likelihood <code>weight(x)</code>. The probability of each item being selected is
|
||
therefore <code>weight(x) / s</code>, where <code>s</code> is the sum of all <code>weight(x)</code>.</p>
|
||
<p>For slices of length <code>n</code>, complexity is <code>O(n)</code>.
|
||
For more information about the underlying algorithm,
|
||
see the <a href="../distr/weighted/struct.WeightedIndex.html" title="struct rand::distr::weighted::WeightedIndex"><code>WeightedIndex</code></a> distribution.</p>
|
||
<p>See also <a href="trait.IndexedMutRandom.html#method.choose_weighted_mut" title="method rand::seq::IndexedMutRandom::choose_weighted_mut"><code>choose_weighted_mut</code></a>.</p>
|
||
<h5 id="example-3"><a class="doc-anchor" href="#example-3">§</a>Example</h5>
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::prelude::<span class="kw-2">*</span>;
|
||
|
||
<span class="kw">let </span>choices = [(<span class="string">'a'</span>, <span class="number">2</span>), (<span class="string">'b'</span>, <span class="number">1</span>), (<span class="string">'c'</span>, <span class="number">1</span>), (<span class="string">'d'</span>, <span class="number">0</span>)];
|
||
<span class="kw">let </span><span class="kw-2">mut </span>rng = rand::rng();
|
||
<span class="comment">// 50% chance to print 'a', 25% chance to print 'b', 25% chance to print 'c',
|
||
// and 'd' will never be printed
|
||
</span><span class="macro">println!</span>(<span class="string">"{:?}"</span>, choices.choose_weighted(<span class="kw-2">&mut </span>rng, |item| item.<span class="number">1</span>).unwrap().<span class="number">0</span>);</code></pre></div></div></details><details class="toggle method-toggle" open><summary><section id="method.choose_multiple_weighted" class="method"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#211-235">Source</a><h4 class="code-header">fn <a href="#method.choose_multiple_weighted" class="fn">choose_multiple_weighted</a><R, F, X>(
|
||
&self,
|
||
rng: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&mut R</a>,
|
||
amount: <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a>,
|
||
weight: F,
|
||
) -> <a class="enum" href="https://doc.rust-lang.org/1.93.1/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="struct" href="struct.SliceChooseIter.html" title="struct rand::seq::SliceChooseIter">SliceChooseIter</a><'_, Self, Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>>, <a class="enum" href="../distr/weighted/enum.Error.html" title="enum rand::distr::weighted::Error">WeightError</a>><div class="where">where
|
||
Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
|
||
R: <a class="trait" href="../trait.Rng.html" title="trait rand::Rng">Rng</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
|
||
F: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&Self::<a class="associatedtype" href="https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html#associatedtype.Output" title="type core::ops::index::Index::Output">Output</a>) -> X,
|
||
X: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/convert/trait.Into.html" title="trait core::convert::Into">Into</a><<a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.f64.html">f64</a>>,</div></h4></section></summary><div class="docblock"><p>Biased sampling of <code>amount</code> distinct elements</p>
|
||
<p>Similar to <a href="trait.IndexedRandom.html#method.choose_multiple" title="method rand::seq::IndexedRandom::choose_multiple"><code>choose_multiple</code></a>, but where the likelihood of each
|
||
element’s inclusion in the output may be specified. Zero-weighted
|
||
elements are never returned; the result may therefore contain fewer
|
||
elements than <code>amount</code> even when <code>self.len() >= amount</code>. The elements
|
||
are returned in an arbitrary, unspecified order.</p>
|
||
<p>The specified function <code>weight</code> maps each item <code>x</code> to a relative
|
||
likelihood <code>weight(x)</code>. The probability of each item being selected is
|
||
therefore <code>weight(x) / s</code>, where <code>s</code> is the sum of all <code>weight(x)</code>.</p>
|
||
<p>This implementation uses <code>O(length + amount)</code> space and <code>O(length)</code> time.
|
||
See <a href="index/fn.sample_weighted.html" title="fn rand::seq::index::sample_weighted"><code>index::sample_weighted</code></a> for details.</p>
|
||
<h5 id="example-4"><a class="doc-anchor" href="#example-4">§</a>Example</h5>
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::prelude::<span class="kw-2">*</span>;
|
||
|
||
<span class="kw">let </span>choices = [(<span class="string">'a'</span>, <span class="number">2</span>), (<span class="string">'b'</span>, <span class="number">1</span>), (<span class="string">'c'</span>, <span class="number">1</span>)];
|
||
<span class="kw">let </span><span class="kw-2">mut </span>rng = rand::rng();
|
||
<span class="comment">// First Draw * Second Draw = total odds
|
||
// -----------------------
|
||
// (50% * 50%) + (25% * 67%) = 41.7% chance that the output is `['a', 'b']` in some order.
|
||
// (50% * 50%) + (25% * 67%) = 41.7% chance that the output is `['a', 'c']` in some order.
|
||
// (25% * 33%) + (25% * 33%) = 16.6% chance that the output is `['b', 'c']` in some order.
|
||
</span><span class="macro">println!</span>(<span class="string">"{:?}"</span>, choices.choose_multiple_weighted(<span class="kw-2">&mut </span>rng, <span class="number">2</span>, |item| item.<span class="number">1</span>).unwrap().collect::<Vec<<span class="kw">_</span>>>());</code></pre></div></div></details></div><h2 id="dyn-compatibility" class="section-header">Dyn Compatibility<a href="#dyn-compatibility" class="anchor">§</a></h2><div class="dyn-compatibility-info"><p>This trait is <b>not</b> <a href="https://doc.rust-lang.org/1.93.1/reference/items/traits.html#dyn-compatibility">dyn compatible</a>.</p><p><i>In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.</i></p></div><h2 id="foreign-impls" class="section-header">Implementations on Foreign Types<a href="#foreign-impls" class="anchor">§</a></h2><details class="toggle implementors-toggle"><summary><section id="impl-IndexedRandom-for-%5BT%5D" class="impl"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#364-368">Source</a><a href="#impl-IndexedRandom-for-%5BT%5D" class="anchor">§</a><h3 class="code-header">impl<T> <a class="trait" href="trait.IndexedRandom.html" title="trait rand::seq::IndexedRandom">IndexedRandom</a> for <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.slice.html">[T]</a></h3></section></summary><div class="impl-items"><section id="method.len" class="method trait-impl"><a class="src rightside" href="../../src/rand/seq/slice.rs.html#365-367">Source</a><a href="#method.len" class="anchor">§</a><h4 class="code-header">fn <a href="#tymethod.len" class="fn">len</a>(&self) -> <a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.usize.html">usize</a></h4></section></div></details><h2 id="implementors" class="section-header">Implementors<a href="#implementors" class="anchor">§</a></h2><div id="implementors-list"></div><script src="../../trait.impl/rand/seq/slice/trait.IndexedRandom.js" data-ignore-extern-crates="std" async></script><script type="text/json" id="notable-traits-data">{"SliceChooseIter<'_, Self, Self::Output>":"<h3>Notable traits for <code><a class=\"struct\" href=\"struct.SliceChooseIter.html\" title=\"struct rand::seq::SliceChooseIter\">SliceChooseIter</a><'a, S, T></code></h3><pre><code><div class=\"where\">impl<'a, S: <a class=\"trait\" href=\"https://doc.rust-lang.org/1.93.1/core/ops/index/trait.Index.html\" title=\"trait core::ops::index::Index\">Index</a><<a class=\"primitive\" href=\"https://doc.rust-lang.org/1.93.1/std/primitive.usize.html\">usize</a>, Output = T> + ?<a class=\"trait\" href=\"https://doc.rust-lang.org/1.93.1/core/marker/trait.Sized.html\" title=\"trait core::marker::Sized\">Sized</a> + 'a, T: 'a> <a class=\"trait\" href=\"https://doc.rust-lang.org/1.93.1/core/iter/traits/iterator/trait.Iterator.html\" title=\"trait core::iter::traits::iterator::Iterator\">Iterator</a> for <a class=\"struct\" href=\"struct.SliceChooseIter.html\" title=\"struct rand::seq::SliceChooseIter\">SliceChooseIter</a><'a, S, T></div><div class=\"where\"> type <a href=\"https://doc.rust-lang.org/1.93.1/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item\" class=\"associatedtype\">Item</a> = <a class=\"primitive\" href=\"https://doc.rust-lang.org/1.93.1/std/primitive.reference.html\">&'a T</a>;</div>"}</script></section></div></main></body></html> |