Merge pull request #642 from brian-brazil/sort-nan

Sort NaN as the lowest value.

rules/ast/functions.go

@@ -169,6 +169,9 @@ func (s vectorByValueHeap) Len() int {
 }
 
 func (s vectorByValueHeap) Less(i, j int) bool {
+	if math.IsNaN(float64(s[i].Value)) {
+		return true
+	}
 	return s[i].Value < s[j].Value
 }
 

rules/rules_test.go

@@ -307,6 +307,19 @@ func TestExpressions(t *testing.T) {
 				`http_requests{group="canary", instance="1", job="app-server"} => 800 @[%v]`,
 			},
 			checkOrder: true,
+		}, {
+			expr: `sort(0 / round(http_requests, 400) + http_requests)`,
+			output: []string{
+				`{group="production", instance="0", job="api-server"} => NaN @[%v]`,
+				`{group="production", instance="1", job="api-server"} => 200 @[%v]`,
+				`{group="canary", instance="0", job="api-server"} => 300 @[%v]`,
+				`{group="canary", instance="1", job="api-server"} => 400 @[%v]`,
+				`{group="production", instance="0", job="app-server"} => 500 @[%v]`,
+				`{group="production", instance="1", job="app-server"} => 600 @[%v]`,
+				`{group="canary", instance="0", job="app-server"} => 700 @[%v]`,
+				`{group="canary", instance="1", job="app-server"} => 800 @[%v]`,
+			},
+			checkOrder: true,
 		}, {
 			expr: `sort_desc(http_requests)`,
 			output: []string{