diff --git a/pkg/datasource/functions.go b/pkg/datasource/functions.go
index 62074de..aec2176 100644
--- a/pkg/datasource/functions.go
+++ b/pkg/datasource/functions.go
@@ -2,8 +2,8 @@ package datasource
 
 import (
 	"fmt"
-	"time"
 
+	"github.com/alexanderzobnin/grafana-zabbix/pkg/gtime"
 	"github.com/alexanderzobnin/grafana-zabbix/pkg/timeseries"
 )
 
@@ -11,20 +11,26 @@ var errFunctionNotSupported = func(name string) error {
 	return fmt.Errorf("function not supported: %s", name)
 }
 
-type DataProcessingFunc = func(series timeseries.TimeSeries, params ...string) timeseries.TimeSeries
+type DataProcessingFunc = func(series timeseries.TimeSeries, params ...string) (timeseries.TimeSeries, error)
 
 var funcMap map[string]DataProcessingFunc
 
 func init() {
-	funcMap = make(map[string]DataProcessingFunc)
-	funcMap["groupBy"] = applyGroupBy
+	funcMap = map[string]DataProcessingFunc{
+		"groupBy": applyGroupBy,
+	}
+
 }
 
 func applyFunctions(series []*timeseries.TimeSeriesData, functions []QueryFunction) ([]*timeseries.TimeSeriesData, error) {
 	for _, f := range functions {
 		if applyFunc, ok := funcMap[f.Def.Name]; ok {
 			for _, s := range series {
-				s.TS = applyFunc(s.TS, f.Params...)
+				result, err := applyFunc(s.TS, f.Params...)
+				if err != nil {
+					return nil, err
+				}
+				s.TS = result
 			}
 		} else {
 			err := errFunctionNotSupported(f.Def.Name)
@@ -34,7 +40,32 @@ func applyFunctions(series []*timeseries.TimeSeriesData, functions []QueryFuncti
 	return series, nil
 }
 
-func applyGroupBy(series timeseries.TimeSeries, params ...string) timeseries.TimeSeries {
-	s := series.GroupBy(time.Minute, "avg")
-	return s
+func applyGroupBy(series timeseries.TimeSeries, params ...string) (timeseries.TimeSeries, error) {
+	pInterval := params[0]
+	pAgg := params[1]
+	interval, err := gtime.ParseInterval(pInterval)
+	if err != nil {
+		return nil, err
+	}
+
+	aggFunc := getAggFunc(pAgg)
+	s := series.GroupBy(interval, aggFunc)
+	return s, nil
+}
+
+func getAggFunc(agg string) timeseries.AggFunc {
+	switch agg {
+	case "avg":
+		return timeseries.AggAvg
+	case "max":
+		return timeseries.AggMax
+	case "min":
+		return timeseries.AggMin
+	case "first":
+		return timeseries.AggFirst
+	case "last":
+		return timeseries.AggLast
+	default:
+		return timeseries.AggAvg
+	}
 }
diff --git a/pkg/timeseries/models.go b/pkg/timeseries/models.go
index 65b50ad..4a3b3c7 100644
--- a/pkg/timeseries/models.go
+++ b/pkg/timeseries/models.go
@@ -29,3 +29,5 @@ type TimeSeriesData struct {
 type TimeSeriesMeta struct {
 	Item *zabbix.Item
 }
+
+type AggFunc = func(points []TimePoint) *float64
diff --git a/pkg/timeseries/timeseries.go b/pkg/timeseries/timeseries.go
index a0e58d5..401b6ae 100644
--- a/pkg/timeseries/timeseries.go
+++ b/pkg/timeseries/timeseries.go
@@ -17,7 +17,7 @@ func NewTimeSeriesData() *TimeSeriesData {
 	}
 }
 
-func (tsd *TimeSeriesData) Len() int {
+func (tsd TimeSeriesData) Len() int {
 	return len(tsd.TS)
 }
 
@@ -30,8 +30,94 @@ func (tsd *TimeSeriesData) Add(point TimePoint) *TimeSeriesData {
 	return tsd
 }
 
-func (ts TimeSeries) GroupBy(interval time.Duration, agg string) TimeSeries {
-	return ts
+func (ts TimeSeries) GroupBy(interval time.Duration, aggFunc AggFunc) TimeSeries {
+	if ts.Len() == 0 {
+		return ts
+	}
+
+	groupedSeries := NewTimeSeries()
+	frame := make([]TimePoint, 0)
+	frameTS := ts[0].GetTimeFrame(interval)
+	var pointFrameTs time.Time
+
+	for _, point := range ts {
+		pointFrameTs = point.GetTimeFrame(interval)
+
+		// Iterate over points and push it into the frame if point time stamp fit the frame
+		if pointFrameTs == frameTS {
+			frame = append(frame, point)
+		} else if pointFrameTs.After(frameTS) {
+			// If point outside frame, then we've done with current frame
+			groupedSeries = append(groupedSeries, TimePoint{
+				Time:  frameTS,
+				Value: aggFunc(frame),
+			})
+
+			// Move frame window to next non-empty interval and fill empty by null
+			frameTS = frameTS.Add(interval)
+			for frameTS.Before(pointFrameTs) {
+				groupedSeries = append(groupedSeries, TimePoint{
+					Time:  frameTS,
+					Value: nil,
+				})
+				frameTS = frameTS.Add(interval)
+			}
+			frame = []TimePoint{point}
+		}
+	}
+
+	groupedSeries = append(groupedSeries, TimePoint{
+		Time:  frameTS,
+		Value: aggFunc(frame),
+	})
+
+	return groupedSeries
+}
+
+func AggAvg(points []TimePoint) *float64 {
+	var sum float64 = 0
+	for _, p := range points {
+		if p.Value != nil {
+			sum += *p.Value
+		}
+	}
+	return &sum
+}
+
+func AggMax(points []TimePoint) *float64 {
+	var max *float64 = nil
+	for _, p := range points {
+		if p.Value != nil {
+			if max == nil {
+				max = p.Value
+			} else if *p.Value > *max {
+				max = p.Value
+			}
+		}
+	}
+	return max
+}
+
+func AggMin(points []TimePoint) *float64 {
+	var min *float64 = nil
+	for _, p := range points {
+		if p.Value != nil {
+			if min == nil {
+				min = p.Value
+			} else if *p.Value < *min {
+				min = p.Value
+			}
+		}
+	}
+	return min
+}
+
+func AggFirst(points []TimePoint) *float64 {
+	return points[0].Value
+}
+
+func AggLast(points []TimePoint) *float64 {
+	return points[len(points)-1].Value
 }
 
 // Aligns point's time stamps according to provided interval.