title: Solr return new column derived from calculated value of 2 columns in document
body: <p>Is it possible with Solr to do a calculation based off two fields in the document and return that calculated value as a new field.</p>
  
  <p>for example I have several fields of integer type</p>
  
  <pre><code>&lt;field name="baseData" type="integer" indexed="true" stored="true"/&gt;
  &lt;field name="altData" type="integer" indexed="true" stored="true"/&gt;
  &lt;field name="altData2" type="integer" indexed="true" stored="true"/&gt;
  </code></pre>
  
  <p>I need to query the solr server to get these fields, and return an additional field that is the combined value (baseData - altData). This returned value could also be (baseData - altData2) depending on the query. </p>
  
  <p>I cannot preload this field into the document as I will not know which field to add to baseData until I form the query.  Although this example only has a few columns the project requirements could be combining baseData with any of many other values.</p>
  
  <p>I think I need to get the data from Solr like this so I can do things like sorting on the newly combined field</p>
  
  <p>I have had no luck finding any documentation on how to do this if it is possible.</p>