array_key_first(): to get the first key of an array

key = array_key_first ($input_array);

Example 1

$input=array(1,2,3,4,5);
echo array_key_first($input);

0

Example 2

$input=array('One' =>'First','Two'=>'Second','Three'=>'Third','Fourth');
echo var_dump(array_key_first($input));

string(3) "One"

Getting first key using array_keys()

$input=array('One' =>'First','Two'=>'Second','Three'=>'Third','Fourth');
echo (array_keys($input)[0]);

One

Example 2: Using array_key_first() with Indexed Arrays

Although array_key_first() is often used with associative arrays, it works with indexed arrays as well:

$indexed_array = [10, 20, 30];
echo array_key_first($indexed_array); // Outputs: 0

Example 3: Handling Empty Arrays

If the array is empty, array_key_first() will return NULL. It's useful to check for this condition:

$empty_array = [];
if (is_null(array_key_first($empty_array))) {
    echo "The array is empty.";
}

Use Case: Efficient Retrieval of First Element in Large Arrays

In large arrays, using array_key_first() is more efficient than resetting the internal pointer with *reset()*. This avoids modifying the array's internal state:

$large_array = range(1, 1000000);
$first_key = array_key_first($large_array); // Efficient
echo $large_array[$first_key]; // Output 1 

Example 4: Using array_key_first() in Combination with array_filter()

We can use array_key_first() to quickly retrieve the first key from a filtered array:

$arr = [1, 2, 3, 4, 5];
$filtered = array_filter($arr, function($val) {
    return $val > 3;
});
$first_key = array_key_first($filtered);
echo "First key after filtering: " . $first_key;

First key after filtering: 3

read more on array_keys()

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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