alerting: add count_non_null reducer

makes it possible to have a second condition requering
at least X points of data.

pkg/services/alerting/conditions/reducer.go

@@ -141,6 +141,16 @@ func (s *SimpleReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 				break
 			}
 		}
+	case "count_non_null":
+		for _, v := range series.Points {
+			if v[0].Valid {
+				value++
+			}
+		}
+
+		if value > 0 {
+			allNull = false
+		}
 	}
 
 	if allNull {

pkg/services/alerting/conditions/reducer_test.go

@@ -67,6 +67,35 @@ func TestSimpleReducer(t *testing.T) {
 			So(reducer.Reduce(series).Valid, ShouldEqual, false)
 		})
 
+		Convey("count_non_null", func() {
+			Convey("with null values and real values", func() {
+				reducer := NewSimpleReducer("count_non_null")
+				series := &tsdb.TimeSeries{
+					Name: "test time serie",
+				}
+
+				series.Points = append(series.Points, tsdb.NewTimePoint(null.FloatFromPtr(nil), 1))
+				series.Points = append(series.Points, tsdb.NewTimePoint(null.FloatFromPtr(nil), 2))
+				series.Points = append(series.Points, tsdb.NewTimePoint(null.FloatFrom(3), 3))
+				series.Points = append(series.Points, tsdb.NewTimePoint(null.FloatFrom(3), 4))
+
+				So(reducer.Reduce(series).Valid, ShouldEqual, true)
+				So(reducer.Reduce(series).Float64, ShouldEqual, 2)
+			})
+
+			Convey("with null values", func() {
+				reducer := NewSimpleReducer("count_non_null")
+				series := &tsdb.TimeSeries{
+					Name: "test time serie",
+				}
+
+				series.Points = append(series.Points, tsdb.NewTimePoint(null.FloatFromPtr(nil), 1))
+				series.Points = append(series.Points, tsdb.NewTimePoint(null.FloatFromPtr(nil), 2))
+
+				So(reducer.Reduce(series).Valid, ShouldEqual, false)
+			})
+		})
+
 		Convey("avg of number values and null values should ignore nulls", func() {
 			reducer := NewSimpleReducer("avg")
 			series := &tsdb.TimeSeries{

public/app/features/alerting/alert_def.ts

@@ -51,6 +51,7 @@ var reducerTypes = [
   {text: 'median()', value: 'median'},
   {text: 'diff()', value: 'diff'},
   {text: 'percent_diff()', value: 'percent_diff'},
+  {text: 'count_non_null()', value: 'count_non_null'},
 ];
 
 var noDataModes = [

public/app/features/alerting/partials/alert_tab.html

@@ -42,7 +42,7 @@
 						<span class="gf-form-label query-keyword width-5" ng-if="$index===0">WHEN</span>
 					</div>
           			<div class="gf-form">
-						<query-part-editor class="gf-form-label query-part width-6" part="conditionModel.reducerPart" handle-event="ctrl.handleReducerPartEvent(conditionModel, $event)">
+						<query-part-editor class="gf-form-label query-part width-9" part="conditionModel.reducerPart" handle-event="ctrl.handleReducerPartEvent(conditionModel, $event)">
 						</query-part-editor>
             			<span class="gf-form-label query-keyword">OF</span>
 					</div>