If you are here you are probably already aware that the array_map function doesn’t allow access to array keys in the callback. Having the key other than the value can be extremely useful dealing with associative arrays (arrays with string keys).
I will show you my use case for this solution and the new function I implemented.
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array_map Use Case
A common real-world use case for the PHP array_map function is transforming data from a database query or an API response. For example, suppose you have an array of user data, and you want to format the names of the users or extract a specific piece of information from each user record.
Imagine you have an array of user records, and each record is an associative array with keys like first_name, last_name, and email:
// Array of user data (e.g., from a database query)
$users = [
[
'first_name' => 'John',
'last_name' => 'Doe',
'email' => '[email protected]'
],
[
'first_name' => 'Jane',
'last_name' => 'Smith',
'email' => '[email protected]'
],
[
'first_name' => 'Bob',
'last_name' => 'Johnson',
'email' => '[email protected]'
]
];Scenario 1: extract information
You can easily extract the list of email addresses to send a notification to:
$emails = array_map(function($user) {
return $user['email'];
}, $users);
// Result: ['[email protected]', '[email protected]', '[email protected]']Scenario 2: add information
You can use the array_map function to add new fields to the user object based on their information:
// Using array_map to add the avatar field to each user
$result = array_map(function($user) {
return array_merge(
$user,
[
'avatar' => 'https://eu.ui-avatars.com/api/?background=ff7511&color=fff&name='.$user['first_name']
]
);
}, $users);
// Output the result
var_dump($result);Use Case For Associative Array
I made a data extraction from a NoSQL database to create a chart on my product dashboard. The data I receive from the NoSQL database looks like this:
$data = [
"2024-08-25" => ["doc_count" => 523, "score" => 0.2, "skipped" => 0],
"2024-08-24" => ["doc_count" => 423, "score" => 0.2, "skipped" => 0],
"2024-08-23" => ["doc_count" => 453, "score" => 0.2, "skipped" => 0],
"2024-08-22" => ["doc_count" => 267, "score" => 0.2, "skipped" => 0],
"2024-08-21" => ["doc_count" => 378, "score" => 0.2, "skipped" => 0],
"2024-08-20" => ["doc_count" => 325, "score" => 0.2, "skipped" => 0],
"2024-08-19" => ["doc_count" => 501, "score" => 0.2, "skipped" => 0],
];Because of the javascript library used to visualize charts I need to transform this data into the format below to make the life easier for the frontend developer:
$result = [
[
"label" => "2024-08-25",
"value" => 523
],
[
"label" => "2024-08-24",
"value" => 423
],
...
];But to perform this transformation I need access to the key of the original array to put it into the “label” field. But the default array_map function only allows access the value.
Here’s an implementation of the array_map_assoc function that works with associative arrays. It provides both the key and value as arguments of the callback:
/**
* Apply a mapping callback receiving key and value as arguments.
* The standard array_map doesn't pass the key to the callback. But in the case of associative arrays,
* it could be really helpful.
*
* array_map_assoc(function ($key, $value) {
* ...
* }, $items)
*
* @param callable $callback
* @param array $array
* @return array
*/
function array_map_assoc(callable $callback, array $array): array
{
return array_map(function($key) use ($callback, $array){
return $callback($key, $array[$key]);
}, array_keys($array));
}Now I can transform the original user array in the data format for the javascript chart library:
$histogram = array_map_assoc(function ($key, $value) {
return [
'label' => $key,
'value' => $value['doc_count']
];
}, $data);Note
Be careful because the array_map_assoc function does not preserve the state of the string keys, but it generates a completely new standard array.
I also added this function into the global namespace in my Laravel application as a new helper function:
Why do not use foreach?
More experienced developers are maybe thinking that you can access the key and value simply using a foreach statement:
foreach ($data as $date => $value) {
...
}Using foreach you have to use an additional variable to save the resulting transformation and you can’t structure the code in a “one line” statement.
// Using foreach
$result = [];
foreach ($data as $date => $value) {
$result[] = [
'label' => $date,
'value' => $value['doc_count']
];
}
return $result;
// Using array_map_assoc
return array_map_assoc(function ($key, $value) {
return [
'label' => $key,
'value' => $value['doc_count']
];
}, $data);It’s short and easier to read for me.
For more technical articles you can follow me on Linkedin or X.
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