From f9af4675adc767c3de890e8e20252fdd44e7caf8 Mon Sep 17 00:00:00 2001
From: Jev Forsberg <46619047+baldm0mma@users.noreply.github.com>
Date: Wed, 17 Apr 2024 07:01:13 -0600
Subject: [PATCH] Reducers: Update percentile logic - move percentiles to after
 standard reducers (#86004)

* baldm0mma/pth_fix2/ move percentiles to after standard reducers

* baldm0mma/pth_fix2/ update ordinal suffix

---------

Co-authored-by: nmarrs <nathanielmarrs@gmail.com>
---
 .../src/transformations/fieldReducer.test.ts  | 12 +++---
 .../src/transformations/fieldReducer.ts       | 37 +++++++++++--------
 2 files changed, 29 insertions(+), 20 deletions(-)

diff --git a/packages/grafana-data/src/transformations/fieldReducer.test.ts b/packages/grafana-data/src/transformations/fieldReducer.test.ts
index 7ccda4c1573..f155a62e511 100644
--- a/packages/grafana-data/src/transformations/fieldReducer.test.ts
+++ b/packages/grafana-data/src/transformations/fieldReducer.test.ts
@@ -252,17 +252,19 @@ describe('Stats Calculators', () => {
     expect(reduce(someNulls, ReducerID.count)).toEqual(4);
   });
 
-  for (let i = 1; i < 100; i++) {
-    it(`can reduce the ${i}th percentile`, () => {
+  it('can reduce to percentiles', () => {
+    // This `Array.from` will build an array of elements from 1 to 99
+    const percentiles = [...Array.from({ length: 99 }, (_, i) => i + 1)];
+    percentiles.forEach((percentile) => {
       const preciseStats = reduceField({
         field: createField(
           'x',
           Array.from({ length: 101 }, (_, index) => index)
         ),
-        reducers: [(ReducerID as Record<string, ReducerID>)[`p${i}`]],
+        reducers: [(ReducerID as Record<string, ReducerID>)[`p${percentile}`]],
       });
 
-      expect(preciseStats[`p${i}`]).toEqual(i);
+      expect(preciseStats[`p${percentile}`]).toEqual(percentile);
     });
-  }
+  });
 });
diff --git a/packages/grafana-data/src/transformations/fieldReducer.ts b/packages/grafana-data/src/transformations/fieldReducer.ts
index a08c7db3c50..b3d547184cb 100644
--- a/packages/grafana-data/src/transformations/fieldReducer.ts
+++ b/packages/grafana-data/src/transformations/fieldReducer.ts
@@ -402,27 +402,34 @@ export const fieldReducers = new Registry<FieldReducerInfo>(() => [
     }),
     preservesUnits: false,
   },
+  ...buildPercentileReducers(),
 ]);
 
-for (let i = 1; i < 100; i++) {
-  const percentile = i / 100;
-  const id = `p${i}` as ReducerID;
+// This `Array.from` will build an array of elements from 1 to 99
+const buildPercentileReducers = (percentiles = [...Array.from({ length: 99 }, (_, i) => i + 1)]) => {
+  const percentileReducers: FieldReducerInfo[] = [];
   const nth = (n: number) =>
     n > 3 && n < 21 ? 'th' : n % 10 === 1 ? 'st' : n % 10 === 2 ? 'nd' : n % 10 === 3 ? 'rd' : 'th';
-  const name = `${i}${nth(i)} percentile`;
-  const description = `${i}${nth(i)} percentile value`;
 
-  fieldReducers.register({
-    id: id,
-    name: name,
-    description: description,
-    standard: false,
-    reduce: (field: Field, ignoreNulls: boolean, nullAsZero: boolean): FieldCalcs => {
-      return { [id]: calculatePercentile(field, percentile, ignoreNulls, nullAsZero) };
-    },
-    preservesUnits: true,
+  percentiles.forEach((p) => {
+    const percentile = p / 100;
+    const id = `p${p}` as ReducerID;
+    const name = `${p}${nth(p)} %`;
+    const description = `${p}${nth(p)} percentile value`;
+
+    percentileReducers.push({
+      id: id,
+      name: name,
+      description: description,
+      standard: false,
+      reduce: (field: Field, ignoreNulls: boolean, nullAsZero: boolean): FieldCalcs => {
+        return { [id]: calculatePercentile(field, percentile, ignoreNulls, nullAsZero) };
+      },
+      preservesUnits: true,
+    });
   });
-}
+  return percentileReducers;
+};
 
 // Used for test cases
 export const defaultCalcs: FieldCalcs = {