title: How can check all array keys are include subkey
body: <p>How can check that all keys are include sub key.</p>
  
  <pre><code>$array1 = array("key1"=&gt;"sub1", "key2"=&gt;"sub2"); // true
  
  $array2 = array("key1", "key2"=&gt;"sub2"); // false
  $array3 = array("key1"=&gt;"sub1", "key2"); // false
  $array4 = array("key1", "key2"); // false
  
  if(checkSubKey($array1)) 
      echo "true";
  else
      echo "false";
  </code></pre>
  
  <p>Thanks so much.</p>