title: How to add a Spark Dataframe to the bottom of another dataframe?
body: <p>I can use <code>withcolumn</code>to add new columns to a Dataframe. But in scala how can I add new rows to a DataFrame? </p>
  
  <p>I'm trying to add a dataframe to the bottom of another one. So either how to add rows in scala or how to add a DataFrame to the bottom of another one will help. Thanks</p>