JavaScript - 随机获取数组元素

短命女 2023-02-11 08:59 16阅读 0赞

1.应用场景

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   <td>随机获取数组元素.</td> 
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2.学习/操作

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   <td> <p>1.随机获取数组一个元素</p> 
    <blockquote> 
     <p>var items = ['1','2','4','5','6','7','8','9','10'];</p> 
     <p>var item = items[Math.floor(Math.random()*items.length)];</p> 
    </blockquote> <p><img alt="" height="176" src="https://img-blog.csdnimg.cn/20200522184228819.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dpbGxpYW1fbg==,size_16,color_FFFFFF,t_70" width="489"></p> <p>解释:</p> <p><code>Math.random()</code>返回0到1之间的一个伪随机数，可能等于0，但是一定小于1</p> <p><img alt="" height="180" src="https://img-blog.csdnimg.cn/20200528164958436.png" width="217"></p> <p><code>Math.floor</code>方法返回小于参数值的最大整数（地板值）</p> <p>&nbsp;</p> <p><img alt="" height="107" src="https://img-blog.csdnimg.cn/20200528165043713.png" width="161"></p> <p>&nbsp;</p> <p>结合起来:</p> <p>随机获取一个0-1之间的小数, 然后乘以自身长度, 一定是一个大于等于0 小于自身长度的一个数.&nbsp; 如上面 长度为10， 则获取的一个随机数就为0-10之间的一个数[数组的下标].</p> <p>最后根据下标获取数组元素值即可</p> <p>&nbsp;</p> <p>2.随机获取几个元素</p> 
    <blockquote> 
     <p>function getRandomArrayElements(arr, count) { <br> &nbsp; &nbsp; var shuffled = arr.slice(0), i = arr.length, min = i - count, temp, index;&nbsp; <span style="color:#ffbb66;">//只是声明变量的方式, 也可以分开写</span><br> &nbsp; &nbsp; while (i-- &gt; min) { </p> 
     <p>&nbsp; &nbsp; &nbsp; &nbsp;&nbsp;//console.log(i);<br> &nbsp; &nbsp; &nbsp; &nbsp; index = Math.floor(<span style="color:#f33b45;">(i + 1) * Math.random()</span>); //这里的+1 是因为上面i--的操作&nbsp; 所以要加回来<br> &nbsp; &nbsp; &nbsp; &nbsp;<span style="color:#ffbb66;"> temp = shuffled[index];&nbsp; //即值交换<br> &nbsp; &nbsp; &nbsp; &nbsp; shuffled[index] = shuffled[i];&nbsp;<br> &nbsp; &nbsp; &nbsp; &nbsp; shuffled[i] = temp;</span><br> &nbsp; &nbsp; &nbsp; &nbsp; //console.log(shuffled);<br> &nbsp; &nbsp; }<br> &nbsp; &nbsp; return shuffled.slice(min);<br> }</p> 
     <p><br> var items = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10'];<br> console.log( getRandomArrayElements(items, 4) );</p> 
    </blockquote> <p>截图：</p> <p>&nbsp;</p> <p><img alt="" height="499" src="https://img-blog.csdnimg.cn/20200528175015236.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dpbGxpYW1fbg==,size_16,color_FFFFFF,t_70" width="679"></p> <p>解析:</p> <p>思路就是将新拷贝一份数组, 然后将数组按照获取元素的次数, 每次将元素交换[从倒数第二个开始往前开始, 与随机获取的数组下标元素对调位置], 最后截取数组元素个数 返回结果.&nbsp;</p> <p>&nbsp;</p> <p>&nbsp;</p> <p>&nbsp;</p> <p>后续补充</p> <p>...</p> </td> 
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3.问题/补充

4.参考

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   <td><a href="https://www.cnblogs.com/doseoer/p/5728955.html" rel="nofollow">https://www.cnblogs.com/doseoer/p/5728955.html</a>&nbsp; //js随机从数组中取出几个元素</td> 
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后续补充

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