title: difference between pyspark.pandas.frame.DataFrame and pyspark.sql.dataframe.DataFrame and their conversion
body: <p>I could not find any detailed documentation on this point, so what is the difference between a <code>pyspark.pandas.frame.DataFrame</code> and <code>pyspark.sql.dataframe.DataFrame</code>, and where to find the documentation of their methods?</p>
  <p>Also how to cast, or convert one into the other and vice versa? Is it always seamless to convert them or some data types are not recognised?</p>