Group by doesn't work after value mapping

[allentsliu]

• What Grafana version and what operating system are you using?
  9.0.2, Mac

• What are you trying to achieve?
  Format the data in a column using valuemap then use groupBy transformation for the pie chart

• How are you trying to achieve it?
  I applied two value mappings for the exceptionMessage column. Then, I added 2 transformations. Add Field From Calculation transformation to add the count field and Group by transformation to group by the exceptionMessage.
  

  

• What happened?
  For some reason, the same value doesn’t get merged.

• What did you expect to happen?
  I expect the same value gets merged and shows the proper accumulated count

• Can you copy/paste the configuration(s) that you are having problems with?

• Did you receive any errors in the Grafana UI or in related logs? If so, please tell us exactly what they were.

• Did you follow any online instructions? If so, what is the URL?

[michaelzemanek]

For some reason my rename by regex did not work but value mapping worked. Now the issue that I am having is that I cannot group by a value mapping. Any suggestions?