Print Array Keys in PHP

Habdul Hazeez Feb 17, 2022 PHP PHP Array
  1. Print Array Keys With foreach and array_keys in PHP
  2. Print Array Keys With foreach Key-Value Pairs in PHP
  3. Print Array Keys via a Search Value in PHP
  4. Print Array Keys via Strict Value Search in PHP
Print Array Keys in PHP

This tutorial will teach you different methods that you can use to print the keys of an array. These methods will use PHP foreach and array_keys, a built-in PHP function.

In this approach, we loop through the array with foreach. During the loop, we call array_keys on the array, which will extract the keys from the array.

We can pass the keys to a variable in the foreach loop. Afterward, we extract the keys with foreach and array_keys.

<?php
    $history_makers = array(
        'Father USA' 		=> 'Benjamin Franklin',
        'Electromagnetism' 	=> 'Michael Faraday',
        'Enlightenment' 	=> 'Issac Newton',
        'Tesla Coil' 		=> 'Nikola Tesla',
        'Polonium' 			=> 'Marie Curie'
    );

    // Use array_keys to return all the keys
    // in the array
    foreach (array_keys($history_makers) as $key) {
        echo $key . "<br />";
    }
?>

Output:

Father USA <br />
Electromagnetism <br />
Enlightenment <br />
Tesla Coil <br />
Polonium <br />

The foreach loop with its key-value lets you map a key in the array to its value. You can extract and print the array keys during this process.

We print the array keys via the $key variable in the foreach loop in the code.

<?php
    $history_makers = array(
        'Father USA' 		=> 'Benjamin Franklin',
        'Electromagnetism' 	=> 'Michael Faraday',
        'Enlightenment' 	=> 'Issac Newton',
        'Tesla Coil' 		=> 'Nikola Tesla',
        'Polonium' 			=> 'Marie Curie'
    );

    // Use key-value mapping to return the keys
    // in the array
    foreach ($history_makers as $key => $value) {
        echo $key . "<br />";
    }
?>

Output:

Father USA <br />
Electromagnetism <br />
Enlightenment <br />
Tesla Coil <br />
Polonium <br />

You can pass a string value as the second parameter to the array_keys function. When you do this, array_keys consider this value a needle.

As a result, it will search for every key with this value in the array. It’ll return a list of all keys that match the criteria.

<?php
    $history_makers = array(
        'Father USA' 		=> 'Benjamin Franklin',
        'Electromagnetism' 	=> 'Michael Faraday',
        'Enlightenment' 	=> 'Issac Newton',
        'Tesla Coil' 		=> 'Nikola Tesla',
        'Polonium' 			=> 'Marie Curie'
    );

    /**
     * A string second parameter tells array_keys
     * to return arrays containing the parameter
     */
    $needle = array_keys($history_makers, 'Marie Curie');

    echo "<pre>";
    var_dump($needle);
    echo "</pre>";
?>

Output:

array(1) {
  [0]=>
  string(8) "Polonium"
}

We search for the Marie Curie value in the code sample above. The result is an array with matching keys.

This approach builds on returning array keys via a search value, but we’ll perform a strict search in this case. This strict search means that any value that we pass to the array_keys function must match a value in the array case-for-case.

In this method, you’ll need to pass the third parameter, which is a Boolean value, to array_keys. Array_keys perform a strict comparison when you set this Boolean value to true.

<?php
    $history_makers = array(
        'Father USA' 	=> 'Benjamin Franklin',
        'Electromagnetism' 	=> 'Michael Faraday',
        'Enlightenment' => 'Issac Newton',
        'Tesla Coil' 	=> 'Nikola Tesla',
        'Polonium' 		=> 'Marie Curie'
    );

    /**
     * Here, we use array_keys with a third
     * parameter. The third parameter is a
     * Boolean value that array_key uses for
     * strict comparisons. If set to true,
     * the search value must match a value
     * in the array case-for-case.
     */
    $needle_strict = array_keys($history_makers, 'marie curie', true);

    if ($needle_strict) {
        // This code block will not print anything because
        // in strict comparisons "marie curie" is not
        // equal to "Marie Curie"
        echo "<pre>";
        var_dump($needle_strict);
        echo "</pre>";
    } else {
        echo "You have strict search enabled for
        <code>array_keys</code>.<br/>
        Change your search needle and try again.";
    }
?>

Output:

You have strict search enabled for <code>array_keys</code>. <br/>
Change your search needle and try again.
Habdul Hazeez avatar Habdul Hazeez avatar

Habdul Hazeez is a technical writer with amazing research skills. He can connect the dots, and make sense of data that are scattered across different media.

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