PHP: Find out all the keys with the same value in an associative array

Question

Are there any functions in PHP that help find out all the keys with the same value in an associative array? For example, there is an array as follows:

$data1 = array("Peter" => "1", "Ann" => "1", "Susan" => "2", "Tom"=> "3");

I only want the keys with the value "1" (ie Peter and Ann). Thanks for help.

Answer 1

You can use array_keys with the optional second parameter:

array_keys() returns the keys, numeric and string, from the array.

If the optional search_value is specified, then only the keys for that value are returned. Otherwise, all the keys from the array are returned.

Answer 2

Use array_intersect and array_keys.

$data1 = array("Peter" => "1", "Ann" => "1", "Susan" => "2", "Tom"=> "3");
$find = 1;
Var_dump(array_keys(array_intersect($data1, [$find])));

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