PHP : how to get element from array with key like

Try this :

$filtred = array();

foreach($yourArray as $key => $value)
  if(preg_match('/c_\d/',$key))
    $filtred[] = $value;

print_r($filtred);

Try This

 //your array
    $arr1 = array (
           "y" => 35,
           "x" => 51,
           "z" => 35,
           "c_3" => 4,
           "c_1" => 54,
           "c_6" => 53,
           "c_9" => 52
    );
// Array with keys you want
    $arr2 =  array (
           "c_3" => '',
           "c_1" => '',
           "c_6" => '',
           "c_9" => ''
    );
//use array_intersect_key to find the common  ;)
    print_r(array_intersect_key($arr1,$arr2));

Use array_slice: http://php.net/manual/en/function.array-slice.php if you want just select known keys. Here you have solution for filtering arrays by keys: PHP: How to use array_filter() to filter array keys?

You can try using array_filter().

There are some interesting examples on the php documentation page. One of them covers filtering array keys.