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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 `sample` fn in crate `rand`."><meta name="keywords" content="rust, rustlang, rust-lang, sample"><title>rand::seq::index::sample - 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 fn"><!--[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><div class="sidebar-elems"><p class='location'><a href='../../index.html'>rand</a>::<wbr><a href='../index.html'>seq</a>::<wbr><a href='index.html'>index</a></p><script>window.sidebarCurrent = {name: 'sample', ty: 'fn', 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/index.rs.html#181-221' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='../../index.html'>rand</a>::<wbr><a href='../index.html'>seq</a>::<wbr><a href='index.html'>index</a>::<wbr><a class="fn" href=''>sample</a></span></h1><pre class='rust fn'>pub fn sample<R: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(rng: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>R, length: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>, amount: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.usize.html">usize</a>) -> <a class="enum" href="../../../rand/seq/index/enum.IndexVec.html" title="enum rand::seq::index::IndexVec">IndexVec</a> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../../rand/trait.Rng.html" title="trait rand::Rng">Rng</a>, </span></pre><div class='docblock'><p>Randomly sample exactly <code>amount</code> distinct indices from <code>0..length</code>, and
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return them in random order (fully shuffled).</p>
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<p>This method is used internally by the slice sampling methods, but it can
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sometimes be useful to have the indices themselves so this is provided as
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an alternative.</p>
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<p>The implementation used is not specified; we automatically select the
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fastest available algorithm for the <code>length</code> and <code>amount</code> parameters
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(based on detailed profiling on an Intel Haswell CPU). Roughly speaking,
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complexity is <code>O(amount)</code>, except that when <code>amount</code> is small, performance
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is closer to <code>O(amount^2)</code>, and when <code>length</code> is close to <code>amount</code> then
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<code>O(length)</code>.</p>
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<p>Note that performance is significantly better over <code>u32</code> indices than over
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<code>u64</code> indices. Because of this we hide the underlying type behind an
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abstraction, <code>IndexVec</code>.</p>
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<p>If an allocation-free <code>no_std</code> function is required, it is suggested
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to adapt the internal <code>sample_floyd</code> implementation.</p>
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<p>Panics if <code>amount > length</code>.</p>
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