array_keys()

The array_keys() function returns an array containing all the keys or a subset of the keys of the array provided. array_keys() can operate on both indexed and associative arrays.

Syntax

array_keys($array, $filter_value, $strict)

• $array: The array from which the keys are retrieved.
• $filter_value: Optional parameter used to return a subset of the keys where the value matches the argument provided.
• $strict: Optional parameter to be used with $filter_value. If set to true a strict comparison of the argument passed to $filter_value and the array values is performed. By default $strict is set to false.

Example

The following example extracts all the keys from the array. The array $arr contains numeric and string indexes.

<?php
    $arr = array("hello" => "world", "hi", "greeting" => "welcome", 5 => "hello");
    print_r(array_keys($arr));
?>

The above code results in the following output:

Array
(
    [0] => hello
    [1] => 0
    [2] => greeting
    [3] => 5
)

Codebyte Example

The runnable example demonstrates the use of the two optional parameters $filter_value and $strict. array_keys() is called with the $colors array and $filter_value set to "yellow". Note that the filter is case sensitive.

Observe the affect of the $strict parameter on the subset of keys returned when array_keys() is called with the $numbers array. By performing a strict comparison 5 and "5" are not considered equal since they have different types.

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