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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">☰</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'>−</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> {
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fn <a href='#method.choose' class='fnname'>choose</a><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(self, rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</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>><br> <span class="where">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.choose_multiple_fill' class='fnname'>choose_multiple_fill</a><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> self, <br> rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, <br> buf: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&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> ) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br> <span class="where">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a></span>,
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{ ... }
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<div class='item-spacer'></div> fn <a href='#method.choose_multiple' class='fnname'>choose_multiple</a><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> self, <br> rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, <br> amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br> ) -> <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</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>><br> <span class="where">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a></span>,
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{ ... }
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}</pre></div><div class='docblock'><p>Extension trait on iterators, providing random sampling methods.</p>
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<p>This trait is implemented on all sized iterators, providing methods for
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choosing one or more elements. You must <code>use</code> this trait:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">rand</span>::<span class="ident">seq</span>::<span class="ident">IteratorRandom</span>;
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<span class="kw">fn</span> <span class="ident">main</span>() {
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<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>();
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<span class="kw">let</span> <span class="ident">faces</span> <span class="op">=</span> <span class="string">"😀😎😐😕😠😢"</span>;
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"I am {}!"</span>, <span class="ident">faces</span>.<span class="ident">chars</span>().<span class="ident">choose</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">rng</span>).<span class="ident">unwrap</span>());
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}</pre></div>
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<p>Example output (non-deterministic):</p>
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<pre><code class="language-none">I am 😀!
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</code></pre>
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</div>
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<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><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(self, rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</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>> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>, </span></code></h3><div class='docblock'><p>Choose one element at random from the iterator.</p>
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<p>Returns <code>None</code> if and only if the iterator is empty.</p>
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<p>This method uses [<code>Iterator::size_hint</code>] for optimisation. With an
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accurate hint and where [<code>Iterator::nth</code>] is a constant-time operation
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this method can offer <code>O(1)</code> performance. Where no size hint is
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available, complexity is <code>O(n)</code> where <code>n</code> is the iterator length.
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Partial hints (where <code>lower > 0</code>) also improve performance.</p>
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<p>For slices, prefer [<code>SliceRandom::choose</code>] which guarantees <code>O(1)</code>
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performance.</p>
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</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><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> self, <br> rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, <br> buf: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&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>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>, </span></code></h3><div class='docblock'><p>Collects values at random from the iterator into a supplied buffer
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until that buffer is filled.</p>
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<p>Although the elements are selected randomly, the order of elements in
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the buffer is neither stable nor fully random. If random ordering is
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desired, shuffle the result.</p>
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<p>Returns the number of elements added to the buffer. This equals the length
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of the buffer unless the iterator contains insufficient elements, in which
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case this equals the number of elements available.</p>
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<p>Complexity is <code>O(n)</code> where <code>n</code> is the length of the iterator.
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For slices, prefer [<code>SliceRandom::choose_multiple</code>].</p>
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</div><h3 id='method.choose_multiple' class='method'><code id='choose_multiple.v'>fn <a href='#method.choose_multiple' class='fnname'>choose_multiple</a><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> self, <br> rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, <br> amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br>) -> <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</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>> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>, </span></code></h3><div class='docblock'><p>Collects <code>amount</code> values at random from the iterator into a vector.</p>
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<p>This is equivalent to <code>choose_multiple_fill</code> except for the result type.</p>
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<p>Although the elements are selected randomly, the order of elements in
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the buffer is neither stable nor fully random. If random ordering is
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desired, shuffle the result.</p>
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<p>The length of the returned vector equals <code>amount</code> unless the iterator
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contains insufficient elements, in which case it equals the number of
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elements available.</p>
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<p>Complexity is <code>O(n)</code> where <code>n</code> is the length of the iterator.
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For slices, prefer [<code>SliceRandom::choose_multiple</code>].</p>
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</div></div><span class='loading-content'>Loading content...</span>
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<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<I> IteratorRandom for I <span class="where fmt-newline">where<br> 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>, </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><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(self, rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</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>> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>, </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><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> self, <br> rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, <br> buf: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.slice.html">&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>) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>, </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><R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(<br> self, <br> rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, <br> amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a><br>) -> <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a><Self::<a class="type" href="https://doc.rust-lang.org/nightly/core/iter/traits/iterator/trait.Iterator.htm
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src="../../implementors/rand/seq/trait.IteratorRandom.js">
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