From 1fc57d8fd549c6057a860c0d246a2bb96979443d Mon Sep 17 00:00:00 2001
From: Drew Slobodnjak <60050885+drew08t@users.noreply.github.com>
Date: Wed, 17 Jul 2024 09:25:46 -0700
Subject: [PATCH] Transformations: Fix null for reduceSeriesToRows (#90508)

* Transformations: Fix null for reduceSeriesToRows

* Add tests with null data frames
---
 .../transformers/reduce.test.ts               | 109 ++++++++++++++++++
 .../transformations/transformers/reduce.ts    |   7 +-
 2 files changed, 115 insertions(+), 1 deletion(-)

diff --git a/packages/grafana-data/src/transformations/transformers/reduce.test.ts b/packages/grafana-data/src/transformations/transformers/reduce.test.ts
index 5d66b7ec67f..bae31b5b8f9 100644
--- a/packages/grafana-data/src/transformations/transformers/reduce.test.ts
+++ b/packages/grafana-data/src/transformations/transformers/reduce.test.ts
@@ -27,6 +27,14 @@ const seriesAWithMultipleFields = toDataFrame({
   ],
 });
 
+const seriesAWithAllNulls = toDataFrame({
+  name: 'A',
+  fields: [
+    { name: 'time', type: FieldType.time, values: [3000, 4000, 5000, 6000] },
+    { name: 'temperature', type: FieldType.number, values: [null, null, null, null, null] },
+  ],
+});
+
 const seriesBWithSingleField = toDataFrame({
   name: 'B',
   fields: [
@@ -44,6 +52,14 @@ const seriesBWithMultipleFields = toDataFrame({
   ],
 });
 
+const seriesBWithAllNulls = toDataFrame({
+  name: 'B',
+  fields: [
+    { name: 'time', type: FieldType.time, values: [3000, 4000, 5000, 6000] },
+    { name: 'temperature', type: FieldType.number, values: [null, null, null, null, null] },
+  ],
+});
+
 describe('Reducer Transformer', () => {
   beforeAll(() => {
     mockTransformationsRegistry([reduceTransformer]);
@@ -177,6 +193,99 @@ describe('Reducer Transformer', () => {
     );
   });
 
+  it('reduces multiple data frames, one having all null values', async () => {
+    const cfg = {
+      id: DataTransformerID.reduce,
+      options: {
+        reducers: [ReducerID.first, ReducerID.min, ReducerID.max, ReducerID.last],
+      },
+    };
+
+    await expect(transformDataFrame([cfg], [seriesAWithAllNulls, seriesBWithSingleField])).toEmitValuesWith(
+      (received) => {
+        const processed = received[0];
+        const expected: Field[] = [
+          {
+            name: 'Field',
+            type: FieldType.string,
+            values: ['A temperature', 'B temperature'],
+            config: {},
+          },
+          {
+            name: 'First',
+            type: FieldType.number,
+            values: [NaN, 1],
+            config: {},
+          },
+          {
+            name: 'Min',
+            type: FieldType.number,
+            values: [NaN, 1],
+            config: {},
+          },
+          {
+            name: 'Max',
+            type: FieldType.number,
+            values: [NaN, 7],
+            config: {},
+          },
+          {
+            name: 'Last',
+            type: FieldType.number,
+            values: [NaN, 7],
+            config: {},
+          },
+        ];
+
+        expect(processed.length).toEqual(1);
+        expect(processed[0].length).toEqual(2);
+        expect(processed[0].fields).toEqual(expected);
+      }
+    );
+
+    await expect(transformDataFrame([cfg], [seriesAWithSingleField, seriesBWithAllNulls])).toEmitValuesWith(
+      (received) => {
+        const processed = received[0];
+        const expected: Field[] = [
+          {
+            name: 'Field',
+            type: FieldType.string,
+            values: ['A temperature', 'B temperature'],
+            config: {},
+          },
+          {
+            name: 'First',
+            type: FieldType.number,
+            values: [3, NaN],
+            config: {},
+          },
+          {
+            name: 'Min',
+            type: FieldType.number,
+            values: [3, NaN],
+            config: {},
+          },
+          {
+            name: 'Max',
+            type: FieldType.number,
+            values: [6, NaN],
+            config: {},
+          },
+          {
+            name: 'Last',
+            type: FieldType.number,
+            values: [6, NaN],
+            config: {},
+          },
+        ];
+
+        expect(processed.length).toEqual(1);
+        expect(processed[0].length).toEqual(2);
+        expect(processed[0].fields).toEqual(expected);
+      }
+    );
+  });
+
   it('reduces single data frame with many fields', async () => {
     const cfg = {
       id: DataTransformerID.reduce,
diff --git a/packages/grafana-data/src/transformations/transformers/reduce.ts b/packages/grafana-data/src/transformations/transformers/reduce.ts
index 22b19705a65..ad17991d3bd 100644
--- a/packages/grafana-data/src/transformations/transformers/reduce.ts
+++ b/packages/grafana-data/src/transformations/transformers/reduce.ts
@@ -132,7 +132,12 @@ function reduceSeriesToRows(
 
       for (const info of calculators) {
         const v = results[info.id];
-        calcs[info.id][i] = v;
+        if (v === null) {
+          // NaN ensures proper row index, null results in shift
+          calcs[info.id][i] = NaN;
+        } else {
+          calcs[info.id][i] = v;
+        }
       }
     }