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' => 'john.doe@example.com'
],
[
'first_name' => 'Jane',
'last_name' => 'Smith',
'email' => 'jane.smith@example.com'
],
[
'first_name' => 'Bob',
'last_name' => 'Johnson',
'email' => 'bob.johnson@example.com'
]
];
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: ['john.doe@example.com', 'jane.smith@example.com', 'bob.johnson@example.com']
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']
];
}, $data);
Note
Be careful because the array_map_assoc function does not preserve the state of the string keys, but it generates a completely new standard array.
I also added this function into the global namespace in my Laravel application as a new helper function:
https://inspector.dev/laravel-custom-helper-functions-fast-tips/
Why do not use foreach?
More experienced developers are maybe thinking that you can access the key and value simply using a foreach statement:
foreach ($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);
For more technical articles you can follow me on Linkedin or X.
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Top comments (1)
I don't see the problem with a foreach loop. For me it is a debug point, which makes it easier to inspect the code when things go wrong.
Why do you make the code more difficult than it needs to be?
You can add multiple arrays to the array_map function. Php doesn't care if the multiple arrays come from the same source.