title: groupIdx parameter of spark regexp_extract function
body: <p>I don't understand how last parameter <strong>groupIdx</strong> works in below function, I can't find any details in documentation. I am using this function with groupIdx = 0, when I changed this value to > 0, I've received an error <code>java.lang.IndexOutOfBoundsException: No group 1</code>. Can someone explain how it works and when groupIdx > 0 could be applied?</p>
  
  <pre><code>regexp_extract(e: Column, exp: String, groupIdx: Int): Column
  </code></pre>