array_intersect : intersection of two or more arrays

array_intersect(): values common to arrays

array_intersect() returns values from the first array that are present in every comparison array. Keys from the first array are preserved.

$first = ['red', 'green', 'blue'];
$second = ['green', 'blue', 'yellow'];
$result = array_intersect($first, $second);
print_r($result);

Use array_intersect_assoc() when both keys and values must match.

This function takes two or more arrays as input and then returns the associative array containing all the values in input array ( $array1) that are present in all of the arguments. ( keys are not considered for comparison )

$new_array = array_intersect ($array1, $array2,....);

$array1 : Required , the input array which will be checked.
$array2 : Required , the values to be matched with $array1.

Here values are used for comparison ( Keys are not considered ). ( In array_intersect_assoc() Both values and keys are considered for comparison )

Example 1

$first=array(1,2,3,4);
$second=array(1,2,3,5);
$result1=array_intersect($first,$second);
foreach ($result1 as $key => $val) {
echo "$key -> $val <br>";
}

Output is here.

0 -> 1 
1 -> 2 
2 -> 3

Keys of the first index are retained. ( no re-indexing done here) .

Example 2

$first=array('One' =>1,'Two'=>2,'Three'=>3,'Four'=>'Fourth');
$second=array('One'=>1,'Two'=>2,'Third'=>3);

$result1=array_intersect_assoc($first,$second);
foreach ($result1 as $key => $val) {
echo "$key -> $val <br>";
}

Output is here.

One -> 1 
Two -> 2 
Three -> 3

Example: Associative Arrays

$array1 = ["a" => "green", "b" => "red", "c" => "blue"];
$array2 = ["b" => "green", "c" => "yellow"];
$result = array_intersect($array1, $array2);
print_r($result);  // Output: Array ( [a] => green )

Example: Case-Insensitive Intersections

$array1 = ["Red", "Green", "Blue"];
$array2 = ["red", "green"];
$result = array_intersect(array_map('strtolower', $array1), array_map('strtolower', $array2));
print_r($result);  // Output: Array ( [0] => red [1] => green )

array_uintersect(): intersection of arrays with Custom Comparison Difference between arrays considering values
Array REFERENCE

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array_intersect(): Intersection of two or more arrays