Merge branch 'jsvisa-feature/spread-expr'

CHANGELOG.md

@@ -122,6 +122,7 @@ In order to know if subscription writes are being dropped you should monitor the
 - [#595](https://github.com/influxdata/kapacitor/pull/595): Support counting and summing empty batches to 0.
 - [#596](https://github.com/influxdata/kapacitor/pull/596): Support new group by time offset i.e. time(30s, 5s)
 - [#416](https://github.com/influxdata/kapacitor/issues/416): Track ingress counts by database, retention policy, and measurement. Expose stats via cli.
+- [#586](https://github.com/influxdata/kapacitor/pull/586): Add spread stateful function.
 
 - [#600](https://github.com/influxdata/kapacitor/pull/600): Add close http response after handler laert post
 
@@ -500,8 +501,8 @@ See note on a breaking change in the HTTP API below. #163
 - [#153](https://github.com/influxdata/kapacitor/issues/153): Fix panic if referencing non existant field in MapReduce function.
 - [#138](https://github.com/influxdata/kapacitor/issues/138): Change over to influxdata github org.
 - [#164](https://github.com/influxdata/kapacitor/issues/164): Update imports etc from InfluxDB as per the new meta store/client changes.
-- [#163](https://github.com/influxdata/kapacitor/issues/163): BREAKING CHANGE: Removed the 'api/v1' pathing from the HTTP API so that Kapacitor is 
-    path compatible with InfluxDB. While this is a breaking change the kapacitor cli has been updated accordingly and you will not experience any distruptions unless you 
+- [#163](https://github.com/influxdata/kapacitor/issues/163): BREAKING CHANGE: Removed the 'api/v1' pathing from the HTTP API so that Kapacitor is
+    path compatible with InfluxDB. While this is a breaking change the kapacitor cli has been updated accordingly and you will not experience any distruptions unless you
     were calling the HTTP API directly.
 - [#147](https://github.com/influxdata/kapacitor/issues/147): Compress .tar archives from builds.
 

tick/stateful/functions.go

@@ -87,14 +87,15 @@ func init() {
 
 // Return set of built-in Funcs
 func NewFunctions() Funcs {
-	funcs := make(Funcs, len(statelessFuncs)+2)
+	funcs := make(Funcs, len(statelessFuncs)+3)
 	for n, f := range statelessFuncs {
 		funcs[n] = f
 	}
 
 	// Statefull functions -- need new instance
 	funcs["sigma"] = &sigma{}
 	funcs["count"] = &count{}
+	funcs["spread"] = &spread{min: math.Inf(+1), max: math.Inf(-1)}
 
 	return funcs
 }
@@ -447,6 +448,37 @@ func (s *sigma) Call(args ...interface{}) (interface{}, error) {
 	return math.Abs(x-s.mean) / math.Sqrt(s.variance), nil
 }
 
+type spread struct {
+	min float64
+	max float64
+}
+
+func (s *spread) Reset() {
+	s.min = math.Inf(+1)
+	s.max = math.Inf(-1)
+}
+
+// Computes the running range of all values
+func (s *spread) Call(args ...interface{}) (interface{}, error) {
+	if len(args) != 1 {
+		return 0, errors.New("spread expects exactly one argument")
+	}
+	x, ok := args[0].(float64)
+	if !ok {
+		return nil, ErrNotFloat
+	}
+
+	if x < s.min {
+		s.min = x
+	}
+
+	if x > s.max {
+		s.max = x
+	}
+
+	return s.max - s.min, nil
+}
+
 type minute struct {
 }