PHP array_map() Function

Syntax

array array_map(callable $callback, array $array1, array ...$arrays)

Explanation:

• $callback: A function that is applied to each element of the array.
   
• $array1: The first array on which the function will be applied.
   
• $arrays (optional): Additional arrays can be passed to apply the function to multiple arrays at once.

Parameters

1. callback (required): A function that will be applied to each element of the array.
    
2. array1 (required): The main array whose elements will be processed.
    
3. ...arrays (optional): Additional arrays can be passed for element-wise processing.

Return Value

The array_map() function returns a new array where each element is the result of applying the callback function to the corresponding element(s) of the input array(s).

Example 1: Basic Usage  

Let’s say you have an array of numbers, & you want to square each number. Let’s see how you can do it using `array_map`:  

<?php  
// Define a callback function to square a number  
function square($number) {  
    return $number  $number;  
}  

// Original array  
$numbers = [1, 2, 3, 4, 5];  

// Apply the callback function to each element  
$squaredNumbers = array_map('square', $numbers);  

// Print the result  
print_r($squaredNumbers);  
?>  

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Output:  

Array  
(  
    [0] => 1  
    [1] => 4  
    [2] => 9  
    [3] => 16  
    [4] => 25  
)  

In this example, the `square` function is applied to each element of the `$numbers` array, & the result is a new array with squared values.  

Example 2: Using array_map() with a Simple Function

Let's see a basic example where we use array_map() to square each element in an array:

function square($num) {
    return $num * $num;
}
$numbers = [1, 2, 3, 4, 5];
$squaredNumbers = array_map("square", $numbers);
print_r($squaredNumbers);

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Output:

Array
(
    [0] => 1
    [1] => 4
    [2] => 9
    [3] => 16
    [4] => 25
)

Example 3: Using Anonymous Functions with array_map()

Instead of defining a separate function, we can use an anonymous function:

$numbers = [10, 20, 30, 40];
$squaredNumbers = array_map(function($num) {
    return $num * $num;
}, $numbers);
print_r($squaredNumbers);

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Output:

Array
(
    [0] => 100
    [1] => 400
    [2] => 900
    [3] => 1600
)

Example 4: Using Anonymous Functions  

You can also use anonymous functions (closures) with `array_map` for more concise code. Let’s discuss the same example rewritten using an anonymous function:  

<?php  
// Original array  
$numbers = [1, 2, 3, 4, 5];  
// Apply an anonymous function to square each number  
$squaredNumbers = array_map(function($number) {  
    return $number  $number;  
}, $numbers);  

// Print the result  
print_r($squaredNumbers);  
?>  
```  

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Output: 

Array  
(  
    [0] => 1  
    [1] => 4  
    [2] => 9  
    [3] => 16  
    [4] => 25  
)  

This approach is useful when you don’t want to define a separate function for a one-time operation.  

Example 5: Working with Multiple Arrays  

`array_map` can also handle multiple arrays. The callback function will receive elements from each array as arguments. Let’s take an example where we add corresponding elements from two arrays:  

<?php  
// Define a callback function to add two numbers  
function add($a, $b) {  
    return $a + $b;  
}  

// Original arrays  
$array1 = [1, 2, 3];  
$array2 = [4, 5, 6];  
// Apply the callback function to corresponding elements  
$result = array_map('add', $array1, $array2);  


// Print the result  
print_r($result);  
?>  

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Output:  

Array  
(  
    [0] => 5  
    [1] => 7  
    [2] => 9  
)  

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In this case, the `add` function takes two arguments, & `array_map` applies it to pairs of elements from `$array1` & `$array2`. 

Example 6: Applying array_map() on Multiple Arrays

If multiple arrays are provided, array_map() applies the callback function element-wise:

function add($a, $b) {
    return $a + $b;
}
$array1 = [1, 2, 3];
$array2 = [4, 5, 6];

$sumArray = array_map("add", $array1, $array2);
print_r($sumArray);

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Output:

Array
(
    [0] => 5
    [1] => 7
    [2] => 9
)

Creating an Array of Arrays Using array_map()

We can use array_map() to structure data into an array of arrays. Let’s see an example:

$names = ["Alice", "Bob", "Charlie"];
$ages = [25, 30, 22];
$combinedArray = array_map(null, $names, $ages);
print_r($combinedArray);

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Output:

Array
(
    [0] => Array ( [0] => Alice [1] => 25 )
    [1] => Array ( [0] => Bob [1] => 30 )
    [2] => Array ( [0] => Charlie [1] => 22 )
)

Here, null as a callback function groups corresponding elements from both arrays into a new array.

Frequently Asked Questions

What happens if the arrays passed to array_map() have different lengths?

If the arrays have different lengths, array_map() stops processing when the shortest array ends.

Can we use built-in PHP functions with array_map()?

Yes, you can pass PHP built-in functions like strtoupper or abs directly as a callback.

What is the difference between array_map() and array_walk()?

array_map() returns a new array, while array_walk() modifies the original array in place.

Conclusion

In this article, we learned about the PHP array_map() function, how it works, and how to use it to modify array elements efficiently. This function helps apply a callback to each array value, making code cleaner and more readable. Understanding array_map() allows developers to write optimized and maintainable PHP programs with less effort.