Why doesn't PHP remove duplicate merged arrays?

In PHP, you can use the array_merge_recursive() function to realize the merge array operation without deduplication; when this function merges one or more arrays, it will recursively form an array with values ​​with the same key name. The syntax format is "array_merge_recursive(array1,array2,array3...)".

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

Generally when we perform array merging operations, we will Use the " " operator or array_merge() function to achieve this. However, when two or more array elements have the same key name, these two methods will use the last element to overwrite other elements (that is, deduplication and retaining only one element).

How to merge arrays without removing duplicates and retaining duplicate key values?

PHP provides a function, which is the array_merge_recursive() function. When two or more array elements have the same key name, this function will not overwrite the key name, but will recursively form multiple values ​​with the same key name into an array.

Syntax: array_merge_recursive(array1,array2,array3...)

Let’s take a look at the following example:

<?php
$a1=array("a"=>"red","b"=>"green");
$a2=array("c"=>"blue","b"=>"yellow");
var_dump(array_merge_recursive($a1,$a2));
?>

Output results :

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