Limit: Invalidate field reducer calcs on applying limit transformation (#106723)

* fix: clear state calcs when limit transformation is applied

* chore: fix limit tests expected values

packages/grafana-data/src/transformations/transformers/limit.test.ts

@@ -35,18 +35,21 @@ describe('Limit transformer', () => {
         {
           name: 'time',
           type: FieldType.time,
+          state: { calcs: undefined },
           values: [3000, 4000, 5000],
           config: {},
         },
         {
           name: 'message',
           type: FieldType.string,
+          state: { calcs: undefined },
           values: ['one', 'two', 'two'],
           config: {},
         },
         {
           name: 'values',
           type: FieldType.number,
+          state: { calcs: undefined },
           values: [1, 2, 2],
           config: {},
         },
@@ -79,18 +82,21 @@ describe('Limit transformer', () => {
         {
           name: 'time',
           type: FieldType.time,
+          state: { calcs: undefined },
           values: [6000, 7000, 8000],
           config: {},
         },
         {
           name: 'message',
           type: FieldType.string,
+          state: { calcs: undefined },
           values: ['three', 'three', 'three'],
           config: {},
         },
         {
           name: 'values',
           type: FieldType.number,
+          state: { calcs: undefined },
           values: [3, 3, 3],
           config: {},
         },

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

@@ -37,6 +37,12 @@ export const limitTransformer: DataTransformerInfo<LimitTransformerOptions> = {
               fields: frame.fields.map((f) => {
                 return {
                   ...f,
+                  // Clear cached field calculations since applying a limit changes the dataset
+                  // and previously computed stats (min, max, mean, etc.) are no longer valid
+                  state: {
+                    ...f.state,
+                    calcs: undefined,
+                  },
                   values:
                     limit >= 0 ? f.values.slice(0, limit) : f.values.slice(f.values.length + limit, f.values.length),
                 };