From 3bd2bdcebbe50aec3cb7de69e3b3b2bce00ef4da Mon Sep 17 00:00:00 2001
From: Leon Sorokin <leeoniya@gmail.com>
Date: Wed, 29 Jun 2022 18:08:42 -0500
Subject: [PATCH] DataFrame: more thorough detection of unsorted values
 (#51602)

---
 .betterer.results                             |  3 --
 .../transformers/joinDataFrames.test.ts       | 14 +++++
 .../transformers/joinDataFrames.ts            | 52 ++++++++++++-------
 3 files changed, 46 insertions(+), 23 deletions(-)

diff --git a/.betterer.results b/.betterer.results
index 91a50fdcaff..d5ce121e6fb 100644
--- a/.betterer.results
+++ b/.betterer.results
@@ -625,9 +625,6 @@ exports[`better eslint`] = {
       [315, 14, 3, "Unexpected any. Specify a different type.", "193409811"],
       [315, 22, 3, "Unexpected any. Specify a different type.", "193409811"]
     ],
-    "packages/grafana-data/src/transformations/transformers/joinDataFrames.ts:1554585514": [
-      [340, 13, 3, "Unexpected any. Specify a different type.", "193409811"]
-    ],
     "packages/grafana-data/src/transformations/transformers/labelsToFields.test.ts:1352052528": [
       [393, 13, 3, "Unexpected any. Specify a different type.", "193409811"]
     ],
diff --git a/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts b/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts
index 2f78fa5c901..4fb552b0f26 100644
--- a/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts
+++ b/packages/grafana-data/src/transformations/transformers/joinDataFrames.test.ts
@@ -294,5 +294,19 @@ describe('align frames', () => {
       expect(isLikelyAscendingVector(new ArrayVector([7, 6, null]))).toBeFalsy();
       expect(isLikelyAscendingVector(new ArrayVector([7, 8, 6]))).toBeFalsy();
     });
+
+    it('ascending first/last', () => {
+      expect(isLikelyAscendingVector(new ArrayVector([10, 20, 30, 5, 15, 7, 43, 29, 11]), 3)).toBeFalsy();
+      expect(
+        isLikelyAscendingVector(new ArrayVector([null, 10, 20, 30, 5, null, 15, 7, 43, 29, 11, null]), 3)
+      ).toBeFalsy();
+    });
+
+    it('null stuffs', () => {
+      expect(isLikelyAscendingVector(new ArrayVector([null, null, 1]), 3)).toBeTruthy();
+      expect(isLikelyAscendingVector(new ArrayVector([1, null, null]), 3)).toBeTruthy();
+      expect(isLikelyAscendingVector(new ArrayVector([null, null, null]), 3)).toBeTruthy();
+      expect(isLikelyAscendingVector(new ArrayVector([null, 1, null]), 3)).toBeTruthy();
+    });
   });
 });
diff --git a/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts b/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts
index 977c6fb2bb8..18b569e0016 100644
--- a/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts
+++ b/packages/grafana-data/src/transformations/transformers/joinDataFrames.ts
@@ -335,34 +335,46 @@ export function join(tables: AlignedData[], nullModes?: number[][]) {
   return data;
 }
 
-// Quick test if the first and last points look to be ascending
+// Test a few samples to see if the values are ascending
 // Only exported for tests
-export function isLikelyAscendingVector(data: Vector): boolean {
-  let first: any = undefined;
+export function isLikelyAscendingVector(data: Vector, samples = 50) {
+  const len = data.length;
 
-  for (let idx = 0; idx < data.length; idx++) {
-    const v = data.get(idx);
-    if (v != null) {
-      if (first != null) {
-        if (first > v) {
-          return false; // descending
-        }
-        break;
-      }
-      first = v;
-    }
+  // empty or single value
+  if (len <= 1) {
+    return true;
+  }
+
+  // skip leading & trailing nullish
+  let firstIdx = 0;
+  let lastIdx = len - 1;
+
+  while (firstIdx <= lastIdx && data.get(firstIdx) == null) {
+    firstIdx++;
   }
 
-  let idx = data.length - 1;
-  while (idx >= 0) {
-    const v = data.get(idx--);
+  while (lastIdx >= firstIdx && data.get(lastIdx) == null) {
+    lastIdx--;
+  }
+
+  // all nullish or one value surrounded by nullish
+  if (lastIdx <= firstIdx) {
+    return true;
+  }
+
+  const stride = Math.max(1, Math.floor((lastIdx - firstIdx + 1) / samples));
+
+  for (let prevVal = data.get(firstIdx), i = firstIdx + stride; i <= lastIdx; i += stride) {
+    const v = data.get(i);
+
     if (v != null) {
-      if (first > v) {
+      if (v <= prevVal) {
         return false;
       }
-      return true;
+
+      prevVal = v;
     }
   }
 
-  return true; // only one non-null point
+  return true;
 }