Syntax for getting plain field value in computed field
I'd suggest you to start by understanding the structure of your entity. You could do something like &lt;pre&gt;&lt;?php print_r($entity); ?&gt;&lt;/pre&gt; to print on screen your entity object and understand how to reference each one of its fields. 

You'll discover that you could get your title just by using $entity-&gt;title (in your example you are getting the first letter because you are treating it as an array).  You could also find that not all your fields might be have by the 'value' key.

Once you do that, you could get the fields values using field_get_items(). A basic example:

$items = field_get_items('node', $entity, 'field_keywords', $entity-&gt;language);
$item = array_shift($items);
$keywords = $item['value'];


And maybe you could take it one step further and wrap that in a reusable function:

/**
 * Get a node field's first value.
 */
function YOUR_MODULE_node_get_field_single_value($node, $field_name, $key) {
  $items = field_get_items('node', $node, $field_name, $node-&gt;language);

  if (!empty($items)) {
    $item = array_shift($items);
    return isset($item[$key]) ? $item[$key] : NULL;
  }
  else {
    return NULL;
  }
}


And call it like this (assuming that this field has a single value in it):

$keywords = YOUR_MODULE_node_get_field_single_value($entity, 'field_keywords', 'value');


Please note that the above function is just an example, your field might have multiple values in it. In that case, you'll need to iterate the array returned by field_get_items.