Data lookup table with Redis and API call

This class' function is to change a given array's data into an ID. The list is set by a configuration file. I have DI the outer array and objects into the class so that if there are any dependencies - it gets injected.

The protected $_api; is an external API class that contains some API call to an external address that will do a look up given type and value. It returns an ID and if there is a rare chance that it doesn't - it will return null.

redis is a redis object that communicates with redis (it's being instantiated with a known lib so the set/get that you will see in the code are known).

table is the list of tables being looked up.

2 steps:

1. Go find in redis and see if the hash value is there - if it is we get the ID and we move on.

2. If it is not there - go call the API and fetch it, and insert it into redis

My code used to pass the function getID and have that function do the look up / API call, however since I need several values - I decided to do mGET to get multiple values and only make one trip to redis.

The code works, however, I want to transform it to something better utilizing SOLID, and that's where the mGET got me and I'm stuck. I figure that after writing this code I can see it, but I can't which is what I need help on.

class LookUp
{
    protected $_api;
    protected $_redis;
    protected $_tables_switch_id;

    public function __construct(\Redis $redis, Api\Track $api, $tables = array())
    {
        $this->_api = $api;
        $this->_redis = $redis;
        $this->_tables_switch_id = $tables;
    }
    public function changeDataIntoId($data)
    {
        $hash_value = array();
        $index_array = array();
        foreach ($this->_tables_switch_id as $index => $table) {
            if (isset($data[$index])) {
                $hash_value[$index] = md5(serialize(array($index => strtolower($data[$index]))));
                $index_array[] = $index;
            }
        }

        $ids = $this->_redis->mGet($hash_value);
        $i = 0;
        foreach ($ids as $id) {
            $breakdown = $index_array[$i];
            if ($id !== false) {
                $data[$breakdown] = $id;
            } else {

                $api_id = $this->_api->getBreakdownID($breakdown, $data[$breakdown]);
                if ($api_id == null) {
                    $api_id = 0;
                }
                $this->_redis->set($hash_value[$breakdown], $api_id);
                $data[$breakdown] = $api_id;
            }
            $i++;
        }
        return $data;
    }
}

One observation that might confuse you: why do I have two arrays.

One is the hash data, and the other one is an index. The entering data ($data) could be composed of numerous indexes. I'm only converting those who are from $table. This is the sole reason why I must retain the list and why I am also checking for isset.