What function does PHP use to exchange array keys and values?

php uses the "array_flip()" function to exchange array keys and values. The array_flip() function is used to exchange the key names in the array and the corresponding associated key values. The syntax is "array_flip(array);". The parameter array represents the array to be exchanged for key and value pairs; if the exchange is successful, the exchanged array is returned. Returns NULL if the exchange fails.

The operating environment of this tutorial: windows7 system, PHP version 8.1, DELL G3 computer

php is used to exchange array keys and values "array_flip()" function.

array_flip() function is used to reverse/exchange the key names in the array and the corresponding associated key values.

array_flip(array);

Parameters	Description
array	Required . Specifies the array whose key/value pairs need to be reversed.

Return value: If the reversal is successful, the reversed array is returned; if the reversal fails, NULL is returned.​

Note: We must remember that the values ​​of the array must be valid keys, i.e. they must be integers or strings. If a value is of the wrong type, a warning will be thrown and the associated key/value pair will not be included in the result.

Example

<?php
header(&#39;content-type:text/html;charset=utf-8&#39;); 
$arr=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");
var_dump($arr);
$result=array_flip($arr);
var_dump($result);
?>

Description: Use the array_flip() function to remove duplicate elements from the array

In PHP, the key name of the array is unique and will not exist repeatedly.

Using this feature, if two values ​​in the array are the same, the last key and value will be retained after reversing the array, which can indirectly achieve deduplication of the array.

<?php
$arr = array("a"=>"a1","b"=>&#39;b1&#39;,"c"=>"a2","d"=>"a1");
$arr1 = array_flip($arr);
var_dump($arr1);//先反转一次,去掉重复值,输出Array ( [a1] => d [b1] => b [a2] => c )
$arr2 = array_flip($arr1);
var_dump($arr2);//再反转回来,得到去重后的数组,输出Array ( [a] => a1 [b] => b1 [c] => a2 )
$arr3 = array_unique($arr);
var_dump($arr3);//利用php的array_unique函数去重,输出Array ( [a] => a1 [b] => b1 [c] => a2 )
?>

The difference between the two methods is that array_flip gets the last key and value of the repeated element, and array_unique gets the first key and value of the two repeated elements. .

Extended knowledge: Without using a function, you can also use the foreach statement and an empty array to exchange array keys and values

<?php
$arr = array("a"=>"a1","b"=>&#39;b1&#39;,"c"=>"a2","d"=>"a1");
var_dump($arr);
$res=[];
foreach($arr as $k=>$v){
	$res[$v]=$k;
}
var_dump($res);
?>

Recommended learning: "PHP Video Tutorial"

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