Regarding the problem of poor collection communication between array_diff and array_intersect in PHP

Excuse me when defining the following content

<code>$a1=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");
$a2=array("e"=>"red","f"=>"green","g"=>"blue");

$result=array_diff($a1,$a2);
print_r($result);</code>

The returned difference set is Array ([d] => yellow)
But if they are reversed and $a2 is placed in front, why can’t the difference set be found

<code>$result=array_diff($a2,$a1);</code>

Reply content:

Excuse me when defining the following content

<code>$a1=array("a"=>"red","b"=>"green","c"=>"blue","d"=>"yellow");
$a2=array("e"=>"red","f"=>"green","g"=>"blue");

$result=array_diff($a1,$a2);
print_r($result);</code>

The returned difference set is Array ([d] => yellow)
But if they are reversed and $a2 is placed in front, why can’t the difference set be found

<code>$result=array_diff($a2,$a1);</code>

difference sets are in order, just like 4 - 3 is not equal to 3 - 4. This example is not very reasonable, so you will think that you can't find the difference set. In fact, the difference set between $a2 and $a1 is empty, so it looks like there is no difference set. You can use $b = array("e"=>"red","f"=>"green","g"=>"blue","h"=>"gray"); so you can immediately understand what the difference set is.

array array_diff ( array $array1 , array $array2 )
Difference returns values ​​that are in array1 but not in array2 and any other parameter arrays.
After the inversion, of course there is no more

Read the manual carefully

http://www.w3school.com.cn/php/func_array_diff.asp

Thanks for the invitation. The references from the people above are enough for you. array_diff