PHP函数array_flip()在重复数组元素删除中的作用

我们都知道，PHP函数array_flip()格式:

<ol class="dp-xml"><li class="alt"><span><span>array array_flip ( array trans ) <br>//array_flip -- 交换数组中的键和值 </span></span></li></ol>

array array_flip ( array trans ) //array_flip -- 交换数组中的键和值

方法如下：

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">arr</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array</font></span><span>(…………) ;//假设有一万个元素的数组，里面有重复的元素。   </span></span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">arr</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array_flip</font></span><span>(array_flip($arr)); //这样便可以删除重复元素。 </span>
</li>
</ol>

究竟是怎么回事呢？来看下array_flip()的作用：PHP函数array_flip()用于将一个数组的每个元素的键和值交换，如：

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array</font></span><span> ("age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 30, "name" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "php自学网");   </span></span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">arr2</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array_flip</font></span><span>($arr1);　//$arr2 就是 array(</span><span class="attribute"><font color="#ff0000">30</font></span><span> =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "age", "php自学网" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "name");  </span>
</li>
</ol>

在ＰＨＰ的数组中，允许不同的元素可以取同一个值，但不允许同一个键名被不同的元素使用，如：

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array</font></span><span> ("age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 30, "name" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "php自学网", "age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 20);　"age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 20将会取代"age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 30   </span></span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array</font></span><span> ("name" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "php自学网", "age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 45);   </span>
</li>
</ol>

这里 $arr1与$arr2　是相等的。

于是，我们便可以知道，为什么 array_flip(array_flip($arr))　可以删除数组中重复的元素了。首先，$arr里的值会变成键名，因为值是有重复的，变成键名之后这些重复的值便成了重复的键名，ＰＨＰ引擎将重复的键名删除，只保留最后一个。如：

<ol class="dp-xml">
<li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array</font></span><span> ("age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 30, "name" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "php自学网", "age" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> 20);   </span></span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array_flip</font></span><span>($arr1); //$arr1 变成了 array("php自学网" =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "name", </span><span class="attribute"><font color="#ff0000">20</font></span><span> =</span><span class="tag"><strong><font color="#006699">></font></strong></span><span> "age");   </span>
</li>
<li class="alt"><span>//再把 $arr1 的键名与值还复：   </span></li>
<li class="">
<span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array_flip</font></span><span>($arr1);   </span>
</li>
</ol>

上面PHP函数array_flip()的代码写得简洁一些就是：

<ol class="dp-xml"><li class="alt"><span><span>$</span><span class="attribute"><font color="#ff0000">arr1</font></span><span> = </span><span class="attribute-value"><font color="#0000ff">array_flip</font></span><span>(array_flip($arr1));   </span></span></li></ol>