PHP array_map for associative array – Fast Tips

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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