title: Scala Spark: Extract name of the array-typed column
body: <p>I have a schema that looks like following:</p>
  <pre><code> |-- test: struct (nullable = true)
   |    |-- MOB: array (nullable = true)
  </code></pre>
  <p>Is it possible to extract the name of the array which is <code>MOB</code>?</p>