title: Change schema of Spark Dataframe
body: <p>I have a <code>DataFrame[SimpleType]</code>. SimpleType is a class that contains 16 fields. But I have to change it into <code>DataFrame[ComplexType]</code>.</p>
  <p>I've got only schema of ComplexType(there is more than 400 fields), there is no case class for this type. I know mapping neccesary fields (but I don't know how to map it from <code>DataFrame[SimpleType] -&gt; DataFrame[ComplexType]</code>), the rest fields I want to leave as nulls. Does anyone know how to do this in most efficent way?</p>
  <p>Thanks</p>
  <h1>edit</h1>
  <pre><code>class SimpleType{
  field1
  field2
  field3
  field4
  .
  .
  .
  field16
  }
  </code></pre>
  <p>I have got DataFrame that contains this simple type. Also I have a schema of complex type.
  I want to convert this <code>DataFrame[SimpleType] -&gt; Dataframe[ComplexType]</code></p>