How Can I Filter Associative Array Keys Based on Indexed Array Values in PHP?

Filter Associative Array Keys Based on Indexed Array Values

Many programmers encounter the challenge of selectively filtering out keys from an associative array based on specific values stored in an indexed array. In PHP, the array_filter() callback function only provides access to array values, leaving out the key-matching functionality.

Consider the following scenario where $my_array contains key-value pairs:

$my_array = ["foo" => 1, "hello" => "world"];

And $allowed is a simple indexed array with allowed keys:

$allowed = ["foo", "bar"];

The goal is to modify $my_array such that it only contains keys that are also present in $allowed. The desired output is:

$my_array = ["foo" => 1];

To achieve this, we can leverage the array_intersect_key() and array_flip() functions:

var_dump(array_intersect_key($my_array, array_flip($allowed)));

Explanation:

• **array_flip($allowed)**: Reverses the keys and values of $allowed, converting it to an associative array where the original keys become values and vice versa. This allows us to compare keys from $my_array to values in the flipped array.
• array_intersect_key($my_array, $reversed): Intersects the keys of $my_array with the flipped $allowed array. This retains only the keys from $my_array that are present as values in the flipped array, effectively filtering out undesired keys.

By combining these functions, we can selectively remove keys from the associative array based on values in the indexed array without manually iterating through the keys and comparing them.

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