解析PHP函数array_flip()在重复数组元素删除中的作用
我们都知道,PHP中的数组元素删除的方式可以有很多种,经常用到的函数有php中array_unique()。那么我们今天为大家介绍的PHP函数array_flip()在删除数组重复元素时的效率要比array_unique()函数高出大约5倍左右。
PHP函数array_flip()格式:
复制代码 代码如下:
array array_flip ( array trans )
//array_flip -- 交换数组中的键和值
array array_flip ( array trans ) //array_flip -- 交换数组中的键和值
方法如下:
复制代码 代码如下:
$arr = array(…………) ;//假设有一万个元素的数组,里面有重复的元素。
$arr = array_flip(array_flip($arr)); //这样便可以删除重复元素。
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:
复制代码 代码如下:
$arr1 = array ("age" => 30, "name" => "脚本之家");
$arr2 = array_flip($arr1); //$arr2 就是 array(30 => "age", "脚本之家" => "name");
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:
复制代码 代码如下:
$arr1 = array ("age" => 30, "name" => "脚本之家", "age" => 20); "age" => 20将会取代"age" => 30
$arr1 = array ("name" => "脚本之家", "age" => 20);
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:
复制代码 代码如下:
$arr1 = array ("age" => 30, "name" => "脚本之家", "age" => 20);
$arr1 = array_flip($arr1); //$arr1 变成了 array("脚本之家" => "name", 20 => "age");
//再把 $arr1 的键名与值还复:
$arr1 = array_flip($arr1);
上面PHP函数array_flip()的代码写得简洁一些就是:
复制代码 代码如下:
$arr1 = array_flip(array_flip($arr1));

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