feat(transformations): filter selection

packages/grafana-data/src/transformations/transformers/groupBy.ts

@@ -10,7 +10,7 @@ import { FieldMatcherID } from '../matchers/ids';
 import { DataTransformerID } from './ids';
 import { findMaxFields } from './utils';
 
-const MINIMUM_FIELDS_REQUIRED = 2;
+const MINIMUM_FIELDS_REQUIRED = 1;
 
 export enum GroupByOperationID {
   aggregate = 'aggregate',

public/app/features/transformers/editors/GroupByTransformerEditor.tsx

@@ -132,6 +132,9 @@ const GroupByFieldConfiguration = ({ fieldName, config, onConfigChange }: FieldP
             onChange={(stats) => {
               onConfigChange({ ...config, aggregations: stats as ReducerID[] });
             }}
+            filterOptions={(option) =>
+              config?.operation === GroupByOperationID.groupBy ? option.id === ReducerID.count : true
+            }
           />
         )}
       </Stack>