From 0f2284d5e6cc130ba4a7cf449aa00fddd8b93b82 Mon Sep 17 00:00:00 2001
From: Kristina <kristina.durivage@grafana.com>
Date: Mon, 7 Jul 2025 12:05:55 -0500
Subject: [PATCH] Transformations: Reduce > Reduce fields should not persist
 labels between reducers (#107590)

Reduce fields should not persist labels updates between reducers
---
 .../transformers/reduce.test.ts               | 60 ++++++++++++++++++-
 .../transformations/transformers/reduce.ts    |  3 +-
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/packages/grafana-data/src/transformations/transformers/reduce.test.ts b/packages/grafana-data/src/transformations/transformers/reduce.test.ts
index bae31b5b8f9..f50072e0f30 100644
--- a/packages/grafana-data/src/transformations/transformers/reduce.test.ts
+++ b/packages/grafana-data/src/transformations/transformers/reduce.test.ts
@@ -8,7 +8,7 @@ import { notTimeFieldMatcher } from '../matchers/predicates';
 import { transformDataFrame } from '../transformDataFrame';
 
 import { DataTransformerID } from './ids';
-import { reduceFields, reduceTransformer, ReduceTransformerOptions } from './reduce';
+import { reduceFields, reduceTransformer, ReduceTransformerMode, ReduceTransformerOptions } from './reduce';
 
 const seriesAWithSingleField = toDataFrame({
   name: 'A',
@@ -582,4 +582,62 @@ describe('Reducer Transformer', () => {
       `);
     });
   });
+
+  it('reduce fields mode keeps distinct label values with multiple reducers', async () => {
+    const cfg: DataTransformerConfig<ReduceTransformerOptions> = {
+      id: DataTransformerID.reduce,
+      options: {
+        mode: ReduceTransformerMode.ReduceFields,
+        reducers: [ReducerID.max, ReducerID.count],
+        labelsToFields: false,
+      },
+    };
+
+    const seriesA = toDataFrame({
+      length: 3,
+      fields: [{ name: 'value', config: {}, labels: { category: 'apple' }, type: FieldType.number, values: [3, 4, 5] }],
+    });
+
+    const seriesB = toDataFrame({
+      fields: [
+        { name: 'value', config: {}, labels: { category: 'orange' }, type: FieldType.number, values: [6, 7, 8] },
+      ],
+    });
+
+    await expect(transformDataFrame([cfg], [seriesA, seriesB])).toEmitValuesWith((received) => {
+      const processed = received[0];
+
+      expect(processed.length).toEqual(2);
+      expect(processed[0].fields).toMatchInlineSnapshot(`
+        [
+          {
+            "config": {},
+            "labels": {
+              "category": "apple",
+              "reducer": "Max",
+            },
+            "name": "value",
+            "state": undefined,
+            "type": "number",
+            "values": [
+              5,
+            ],
+          },
+          {
+            "config": {},
+            "labels": {
+              "category": "apple",
+              "reducer": "Count",
+            },
+            "name": "value",
+            "state": undefined,
+            "type": "number",
+            "values": [
+              3,
+            ],
+          },
+        ]
+      `);
+    });
+  });
 });
diff --git a/packages/grafana-data/src/transformations/transformers/reduce.ts b/packages/grafana-data/src/transformations/transformers/reduce.ts
index dba2bc286e0..f9d2cd01d4c 100644
--- a/packages/grafana-data/src/transformations/transformers/reduce.ts
+++ b/packages/grafana-data/src/transformations/transformers/reduce.ts
@@ -230,10 +230,11 @@ export function reduceFields(data: DataFrame[], matcher: FieldMatcher, reducerId
           const value = results[reducer];
           const copy = {
             ...field,
+            labels: { ...field.labels },
             type: getFieldType(reducer, field),
             values: [value],
+            state: undefined,
           };
-          copy.state = undefined;
           if (reducers.length > 1) {
             if (!copy.labels) {
               copy.labels = {};