title: set ruby hash element value by array of keys
body: <p>here is what i got:</p>
  
  <pre><code>hash = {:a =&gt; {:b =&gt; [{:c =&gt; old_val}]}}
  keys = [:a, :b, 0, :c]
  new_val = 10
  </code></pre>
  
  <p>hash structure and set of keys can vary.<br>
  i need to get</p>
  
  <pre><code>hash[:a][:b][0][:c] == new_val
  </code></pre>
  
  <p>Thanks!</p>