PHP get previous array element knowing current array key

Question

I have an array with specific keys:

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

In my applicati

Answer 1

@Luca Borrione's solution was helpful. If you want to find both previous and next keys, you may use the following function:

function getAdjascentKey( $key, $hash = array(), $increment ) {
    $keys = array_keys( $hash );    
    $found_index = array_search( $key, $keys );
    if ( $found_index === false ) {
        return false;
    }
    $newindex = $found_index+$increment;
    // returns false if no result found
    return ($newindex > 0 && $newindex < sizeof($hash)) ? $keys[$newindex] : false;
}

Usage:

// previous key
getAdjascentKey( $key, $hash, -1 );

// next key
getAdjascentKey( $key, $hash, +1 );

Examples:

$myhash = array(
    'foo' => 'foovalue',
    'goo' => 'goovalue',
    'moo' => 'moovalue',
    'zoo' => 'zoovalue'
);

getAdjascentKey( 'goo', $myhash, +1 );
// moo

getAdjascentKey( 'zoo', $myhash, +1 );
// false

getAdjascentKey( 'foo', $myhash, -1 );
// false