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<span id="id1"></span><h1>SRANDMEMBER<a class="headerlink" href="#srandmember" title="Permalink to this headline">¶</a></h1>
<p><strong>SRANDMEMBER key [count]</strong></p>
<p>如果命令执行时，只提供了 <code class="docutils literal"><span class="pre">key</span></code> 参数，那么返回集合中的一个随机元素。</p>
<p>从 Redis 2.6 版本开始， <a class="reference internal" href="#srandmember">SRANDMEMBER</a> 命令接受可选的 <code class="docutils literal"><span class="pre">count</span></code> 参数：</p>
<ul class="simple">
<li>如果 <code class="docutils literal"><span class="pre">count</span></code> 为正数，且小于集合基数，那么命令返回一个包含 <code class="docutils literal"><span class="pre">count</span></code> 个元素的数组，数组中的元素<strong>各不相同</strong>。如果 <code class="docutils literal"><span class="pre">count</span></code> 大于等于集合基数，那么返回整个集合。</li>
<li>如果 <code class="docutils literal"><span class="pre">count</span></code> 为负数，那么命令返回一个数组，数组中的元素<strong>可能会重复出现多次</strong>，而数组的长度为 <code class="docutils literal"><span class="pre">count</span></code> 的绝对值。</li>
</ul>
<p>该操作和 <a class="reference internal" href="spop.html#spop"><span>SPOP</span></a> 相似，但 <a class="reference internal" href="spop.html#spop"><span>SPOP</span></a> 将随机元素从集合中移除并返回，而 <a class="reference internal" href="#srandmember">SRANDMEMBER</a> 则仅仅返回随机元素，而不对集合进行任何改动。</p>
<dl class="docutils">
<dt><strong>可用版本：</strong></dt>
<dd>>= 1.0.0</dd>
<dt><strong>时间复杂度:</strong></dt>
<dd><div class="first last line-block">
<div class="line">只提供 <code class="docutils literal"><span class="pre">key</span></code> 参数时为 O(1) 。</div>
<div class="line">如果提供了 <code class="docutils literal"><span class="pre">count</span></code> 参数，那么为 O(N) ，N 为返回数组的元素个数。</div>
</div>
</dd>
<dt><strong>返回值:</strong></dt>
<dd><div class="first last line-block">
<div class="line">只提供 <code class="docutils literal"><span class="pre">key</span></code> 参数时，返回一个元素；如果集合为空，返回 <code class="docutils literal"><span class="pre">nil</span></code> 。</div>
<div class="line">如果提供了 <code class="docutils literal"><span class="pre">count</span></code> 参数，那么返回一个数组；如果集合为空，返回空数组。</div>
</div>
</dd>
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<div class="highlight-python"><div class="highlight"><pre># 添加元素
redis> SADD fruit apple banana cherry
(integer) 3
# 只给定 key 参数，返回一个随机元素
redis> SRANDMEMBER fruit
"cherry"
redis> SRANDMEMBER fruit
"apple"
# 给定 3 为 count 参数，返回 3 个随机元素
# 每个随机元素都不相同
redis> SRANDMEMBER fruit 3
1) "apple"
2) "banana"
3) "cherry"
# 给定 -3 为 count 参数，返回 3 个随机元素
# 元素可能会重复出现多次
redis> SRANDMEMBER fruit -3
1) "banana"
2) "cherry"
3) "apple"
redis> SRANDMEMBER fruit -3
1) "apple"
2) "apple"
3) "cherry"
# 如果 count 是整数，且大于等于集合基数，那么返回整个集合
redis> SRANDMEMBER fruit 10
1) "apple"
2) "banana"
3) "cherry"
# 如果 count 是负数，且 count 的绝对值大于集合的基数
# 那么返回的数组的长度为 count 的绝对值
redis> SRANDMEMBER fruit -10
1) "banana"
2) "apple"
3) "banana"
4) "cherry"
5) "apple"
6) "apple"
7) "cherry"
8) "apple"
9) "apple"
10) "banana"
# SRANDMEMBER 并不会修改集合内容
redis> SMEMBERS fruit
1) "apple"
2) "cherry"
3) "banana"
# 集合为空时返回 nil 或者空数组
redis> SRANDMEMBER not-exists
(nil)
redis> SRANDMEMBER not-eixsts 10
(empty list or set)
</pre></div>
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