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| <h1 class="fqn"><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><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span></h1><span class="out-of-band"> |
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| <div class="docblock item-decl"><pre class="rust fn"><code>pub fn sample<R>(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="enum.IndexVec.html" title="enum rand::seq::index::IndexVec">IndexVec</a> <span class="where fmt-newline">where<br> R: <a class="trait" href="../../trait.Rng.html" title="trait rand::Rng">Rng</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></pre></div><div class="item-info"><div class="stab portability">This is supported on <strong>crate feature <code>alloc</code></strong> only.</div></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Randomly sample exactly <code>amount</code> distinct indices from <code>0..length</code>, and |
| return them in random order (fully shuffled).</p> |
| <p>This method is used internally by the slice sampling methods, but it can |
| sometimes be useful to have the indices themselves so this is provided as |
| an alternative.</p> |
| <p>The implementation used is not specified; we automatically select the |
| fastest available algorithm for the <code>length</code> and <code>amount</code> parameters |
| (based on detailed profiling on an Intel Haswell CPU). Roughly speaking, |
| complexity is <code>O(amount)</code>, except that when <code>amount</code> is small, performance |
| is closer to <code>O(amount^2)</code>, and when <code>length</code> is close to <code>amount</code> then |
| <code>O(length)</code>.</p> |
| <p>Note that performance is significantly better over <code>u32</code> indices than over |
| <code>u64</code> indices. Because of this we hide the underlying type behind an |
| abstraction, <code>IndexVec</code>.</p> |
| <p>If an allocation-free <code>no_std</code> function is required, it is suggested |
| to adapt the internal <code>sample_floyd</code> implementation.</p> |
| <p>Panics if <code>amount > length</code>.</p> |
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