PHP get previous array element knowing current array key -

i have array specific keys:

array(     420 => array(...),      430 => array(...),      555 => array(...) ) 

in application know current key (for example 555). , want previous array element. in example array element key 430. how can in php? tried work prev(), function should know current array element. didn't find function, set current array element.

one option:

to set internal pointer position, have forward (using key , next, maybe reset before make sure start beginning of array):

while(key($array) !== $key) next($array); 

then can use prev():

$prev_val = prev($array); // , key $prev_key = key($array); 

depending on going array afterwards, might want reset internal pointer.

if key not exist in array, have infinite loop, solved with:

 while(key($array) !== null && key($array) !== $key) 

of course prev not give right value anymore assume key searching in array anyway.