From ccbce0c51f05751c7432a3a281fe98587ffa3a1c Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Fri, 30 Sep 2016 10:46:58 +0200
Subject: [PATCH] promql: handle NaN in changes() correctly

---
 promql/functions.go            | 2 +-
 promql/testdata/functions.test | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/promql/functions.go b/promql/functions.go
index 41ff6fe7b..607421470 100644
--- a/promql/functions.go
+++ b/promql/functions.go
@@ -788,7 +788,7 @@ func funcChanges(ev *evaluator, args Expressions) model.Value {
 		prev := model.SampleValue(samples.Values[0].Value)
 		for _, sample := range samples.Values[1:] {
 			current := sample.Value
-			if current != prev {
+			if current != prev && !(math.IsNaN(float64(current)) && math.IsNaN(float64(prev))) {
 				changes++
 			}
 			prev = current
diff --git a/promql/testdata/functions.test b/promql/testdata/functions.test
index cfabb3c9b..a04933110 100644
--- a/promql/testdata/functions.test
+++ b/promql/testdata/functions.test
@@ -50,6 +50,15 @@ eval instant at 50m changes(http_requests[50m])
 
 eval instant at 50m changes(nonexistent_metric[50m])
 
+clear
+
+load 5m
+  x{a="b"} NaN NaN NaN
+  x{a="c"} 0 NaN 0
+
+eval instant at 15m changes(x[15m])
+  {a="b"} 0
+  {a="c"} 2
 
 clear