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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="API documentation for the Rust `IteratorRandom` trait in crate `rand`."><meta name="keywords" content="rust, rustlang, rust-lang, IteratorRandom"><title>rand::seq::IteratorRandom - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="shortcut icon" href="https://www.rust-lang.org/favicon.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow.svg");}</style></head><body class="rustdoc trait"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">&#9776;</div><a href='../../rand/index.html'><div class='logo-container'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk.png' alt='logo'></div></a><p class='location'>Trait IteratorRandom</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#provided-methods">Provided Methods</a><div class="sidebar-links"><a href="#method.choose">choose</a><a href="#method.choose_multiple">choose_multiple</a><a href="#method.choose_multiple_fill">choose_multiple_fill</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>rand</a>::<wbr><a href='index.html'>seq</a></p><script>window.sidebarCurrent = {name: 'IteratorRandom', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press S to search, ? for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>&#x2212;</span>]</a></span><a class='srclink' href='../../src/rand/seq/mod.rs.html#241-375' title='goto source code'>[src]</a></span><span class='in-band'>Trait <a href='../index.html'>rand</a>::<wbr><a href='index.html'>seq</a>::<wbr><a class="trait" href=''>IteratorRandom</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class='rust trait'>pub trait IteratorRandom: <a class="trait" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html" title="trait core::iter::traits::iterator::Iterator">Iterator</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a> {
fn <a href='#method.choose' class='fnname'>choose</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(self, rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a>&lt;Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a></span>,
{ ... }
<div class='item-spacer'></div> fn <a href='#method.choose_multiple_fill' class='fnname'>choose_multiple_fill</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;buf: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&amp;mut [</a>Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">]</a><br>&nbsp;&nbsp;&nbsp;&nbsp;) -&gt; <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a></span>,
{ ... }
<div class='item-spacer'></div> fn <a href='#method.choose_multiple' class='fnname'>choose_multiple</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R, <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br>&nbsp;&nbsp;&nbsp;&nbsp;) -&gt; <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a>&lt;Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a>&gt;<br>&nbsp;&nbsp;&nbsp; <span class="where">where<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a></span>,
{ ... }
}</pre></div><div class='docblock'><p>Extension trait on iterators, providing random sampling methods.</p>
<p>This trait is implemented on all sized iterators, providing methods for
choosing one or more elements. You must <code>use</code> this trait:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">rand</span>::<span class="ident">seq</span>::<span class="ident">IteratorRandom</span>;
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">rng</span> <span class="op">=</span> <span class="ident">rand</span>::<span class="ident">thread_rng</span>();
<span class="kw">let</span> <span class="ident">faces</span> <span class="op">=</span> <span class="string">&quot;😀😎😐😕😠😢&quot;</span>;
<span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;I am {}!&quot;</span>, <span class="ident">faces</span>.<span class="ident">chars</span>().<span class="ident">choose</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">rng</span>).<span class="ident">unwrap</span>());
}</pre></div>
<p>Example output (non-deterministic):</p>
<pre><code class="language-none">I am 😀!
</code></pre>
</div>
<h2 id='provided-methods' class='small-section-header'>Provided methods<a href='#provided-methods' class='anchor'></a></h2><div class='methods'><h3 id='method.choose' class='method'><code id='choose.v'>fn <a href='#method.choose' class='fnname'>choose</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(self, rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a>&lt;Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>,&nbsp;</span></code></h3><div class='docblock'><p>Choose one element at random from the iterator.</p>
<p>Returns <code>None</code> if and only if the iterator is empty.</p>
<p>This method uses [<code>Iterator::size_hint</code>] for optimisation. With an
accurate hint and where [<code>Iterator::nth</code>] is a constant-time operation
this method can offer <code>O(1)</code> performance. Where no size hint is
available, complexity is <code>O(n)</code> where <code>n</code> is the iterator length.
Partial hints (where <code>lower &gt; 0</code>) also improve performance.</p>
<p>For slices, prefer [<code>SliceRandom::choose</code>] which guarantees <code>O(1)</code>
performance.</p>
</div><h3 id='method.choose_multiple_fill' class='method'><code id='choose_multiple_fill.v'>fn <a href='#method.choose_multiple_fill' class='fnname'>choose_multiple_fill</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R, <br>&nbsp;&nbsp;&nbsp;&nbsp;buf: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&amp;mut [</a>Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">]</a><br>) -&gt; <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a> <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>,&nbsp;</span></code></h3><div class='docblock'><p>Collects values at random from the iterator into a supplied buffer
until that buffer is filled.</p>
<p>Although the elements are selected randomly, the order of elements in
the buffer is neither stable nor fully random. If random ordering is
desired, shuffle the result.</p>
<p>Returns the number of elements added to the buffer. This equals the length
of the buffer unless the iterator contains insufficient elements, in which
case this equals the number of elements available.</p>
<p>Complexity is <code>O(n)</code> where <code>n</code> is the length of the iterator.
For slices, prefer [<code>SliceRandom::choose_multiple</code>].</p>
</div><h3 id='method.choose_multiple' class='method'><code id='choose_multiple.v'>fn <a href='#method.choose_multiple' class='fnname'>choose_multiple</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R, <br>&nbsp;&nbsp;&nbsp;&nbsp;amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br>) -&gt; <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a>&lt;Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>,&nbsp;</span></code></h3><div class='docblock'><p>Collects <code>amount</code> values at random from the iterator into a vector.</p>
<p>This is equivalent to <code>choose_multiple_fill</code> except for the result type.</p>
<p>Although the elements are selected randomly, the order of elements in
the buffer is neither stable nor fully random. If random ordering is
desired, shuffle the result.</p>
<p>The length of the returned vector equals <code>amount</code> unless the iterator
contains insufficient elements, in which case it equals the number of
elements available.</p>
<p>Complexity is <code>O(n)</code> where <code>n</code> is the length of the iterator.
For slices, prefer [<code>SliceRandom::choose_multiple</code>].</p>
</div></div><span class='loading-content'>Loading content...</span>
<h2 id='implementors' class='small-section-header'>Implementors<a href='#implementors' class='anchor'></a></h2><div class='item-list' id='implementors-list'><h3 id='impl-IteratorRandom' class='impl'><code class='in-band'>impl&lt;I&gt; IteratorRandom for I <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;I: <a class="trait" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html" title="trait core::iter::traits::iterator::Iterator">Iterator</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,&nbsp;</span></code><a href='#impl-IteratorRandom' class='anchor'></a><a class='srclink' href='../../src/rand/seq/mod.rs.html#478' title='goto source code'>[src]</a></h3><div class='impl-items'><h4 id='method.choose-1' class="method"><code id='choose.v-1'>fn <a href='../../rand/seq/trait.IteratorRandom.html#method.choose' class='fnname'>choose</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(self, rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R) -&gt; <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a>&lt;Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>,&nbsp;</span></code><a class='srclink' href='../../src/rand/seq/mod.rs.html#254-298' title='goto source code'>[src]</a></h4><h4 id='method.choose_multiple_fill-1' class="method"><code id='choose_multiple_fill.v-1'>fn <a href='../../rand/seq/trait.IteratorRandom.html#method.choose_multiple_fill' class='fnname'>choose_multiple_fill</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R, <br>&nbsp;&nbsp;&nbsp;&nbsp;buf: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&amp;mut [</a>Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">]</a><br>) -&gt; <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a> <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>,&nbsp;</span></code><a class='srclink' href='../../src/rand/seq/mod.rs.html#313-335' title='goto source code'>[src]</a></h4><h4 id='method.choose_multiple-1' class="method"><code id='choose_multiple.v-1'>fn <a href='../../rand/seq/trait.IteratorRandom.html#method.choose_multiple' class='fnname'>choose_multiple</a>&lt;R:&nbsp;?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>&gt;(<br>&nbsp;&nbsp;&nbsp;&nbsp;self, <br>&nbsp;&nbsp;&nbsp;&nbsp;rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&amp;mut </a>R, <br>&nbsp;&nbsp;&nbsp;&nbsp;amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br>) -&gt; <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a>&lt;Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" title="type core::iter::traits::iterator::Iterator::Item">Item</a>&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>,&nbsp;</span></code><a class='srclink' href='../../src/rand/seq/mod.rs.html#352-374' title='goto source code'>[src]</a></h4></div></div><span class='loading-content'>Loading content...</span><script type="text/javascript">window.inlined_types=new Set([]);</script><script type="text/javascript" async
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