title: How do I convert table row PCollections to key,value PCollections in Python?
body: <p>There is NO documentation regarding how to convert pCollections into the pCollections necessary for input into .CoGroupByKey()</p>
  
  <p>Context
  Essentially I have two large pCollections and I need to be able to find differences between the two, for type II ETL changes (if it doesn't exist in pColl1 then add to a nested field found in pColl2), so that I am able to retain history of these records from BigQuery. </p>
  
  <p>Pipeline Architecture:</p>
  
  <ol>
  <li>Read BQ Tables into 2 pCollections: dwsku and product. </li>
  <li>Apply a CoGroupByKey() to the two sets to return --> Results </li>
  <li>Parse results to find and nest all changes in dwsku into product. </li>
  </ol>
  
  <p>Any help would be recommended. I found a java link on SO that does the same thing I need to accomplish (but there's nothing on the Python SDK). </p>
  
  <p><a href="https://stackoverflow.com/questions/41243784/convert-from-pcollectiontablerow-to-pcollectionkvk-v">Convert from PCollection&lt;TableRow&gt; to PCollection&lt;KV&lt;K,V&gt;&gt;</a></p>
  
  <p>Is there a documentation / support for Apache Beam, especially Python SDK?</p>