The role of PHP function array_flip() in deleting duplicate array elements_PHP tutorial

We all know, PHP function array_flip() format:

<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 -- exchange the keys and values ​​in the array

as follows:

<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>

What on earth is going on? Let’s take a look at the role of array_flip(): The PHP function array_flip() is used to exchange the key and value of each element of an array, such as:

<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>

In the PＨＰ array, different elements are allowed to take the same value, but the same key name is not allowed to be used by different elements. Such as:

<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>

Here$ arr1 and $arr2 are equal.

So, we can know why array_flip(array_flip($arr)) can delete duplicate elements in the array. First, the value in $arr will become a key name, because the value is repeated. After becoming a key name, these repeated values ​​will become duplicate key names. The PHP engine will delete the duplicate key names and only keep the last one. . Such as:

<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>

The code for the PHP function array_flip() above is written more concisely:

<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>