There are two predefined functions in PHP for applying user defined function on each element of an array.

1. array_walk() : array_walk() applied a user function on each element of an array. It returns TRUE on success and FALSE on failure. The user function takes values and keys of supplied array as parameters.

Syntax : array_walk(array,function,parameters)

Description of function parameters :

array : An array (Required)

function : Name of user function (Required)

parameters : Defined additional parameter for user function (Optional)

Example :

function printAbbreviation($value,$key,$parameter){
    echo $key.$parameter.$value."<br/>";
}

$arr = array( "Sun"=>"Sunday", "Mon"=>"Monday", "Tue"=>"Tuesday", "Fri"=>"Friday" );
array_walk($arr, printAbbreviation," stands for ");

Output :

Sun stands for Sunday
Mon stands for Monday
Tue stands for Tuesday
Fri stands for Friday

2. array_map() : array_map() applied a user defined function to each value of an array and returns a new array with new values retrieved after applying user function. The number of parameters of user function should match the number of arrays passed to the array_map().

Syntax : array_map(function,array1,array2...)

Description of function parameters :

function : Name of user function (or can be null) (Required)

array1 : An array (Required)

array2 : An array (Optional)

Example1 :

function square($param1){
    return $param1*$param1;
}

$numbers = array(2,5,7,10);
$result_array = array_map(square,$numbers);
print_r($result_array);

Output :

Array
(
    [0] => 4
    [1] => 25
    [2] => 49
    [3] => 100
)

Example 2 :

function checkMonth($par1,$par2)
{
     if($par1===$par2)
       {
           return "same";
        }
    return "different";
}

$arr1 = array("Jan","Feb","May","Nov");
$arr2 = array("Jan","June","May","Dec");
$result = array_map("checkMonth",$arr1,$arr2)
print_r($result);

Output :

Array
(
    [0] => same
    [1] => different
    [2] => same
    [3] => different
)