What is the reverse of (object) array (key => value) in PHP?

Question

Is there a fast way to return a key when you know its value in PHP?

For example, if you have:

$Numbers = (object) array ( "0" => 0, "1" => 1, "2" => 3, "3" => 7, "4" => 13 );

is there a way to return:

echo re(13);   // Print 4 

One way I could think of is to build a function specifically for this, but I was wondering if there is a better way.

Answer 1

There is array_search :

$key = array_search(13, (array) $Numbers);

See http://ua2.php.net/array_search

Answer 2

As several other people have mentioned, array_search does what you asked. But if you want an array of ALL the keys that contain the value instead of only the first, you can use array_keys .

print_r(array_keys($Numbers, 13)); // print Array ( [0] => 4 )

http://www.php.net/manual/en/function.array-keys.php

Answer 3

http://php.net/array_search

echo array_search($valToSearch, (array) $Numbers);

Answer 4

if you are certain that you have unique keys:

$flipped = array_flip($array);
$key = $flipped[$knownValue];
return $key;

Otherwise, use array_search:

return array_search($knownValue, $array);

The first approach may be better if you do a number of lookups, and have unique values. The second approach returns the first matching key in case of multiple values.

Answer 5

http://php.net/manual/en/function.array-search.php