Feature/mathandreduce (#41608)

* Added new math functions: round, ceil, floor 
* Added a new reduce function: last.

pkg/expr/mathexp/funcs.go

@@ -53,6 +53,21 @@ var builtins = map[string]parse.Func{
 		VariantReturn: true,
 		F:             isNumber,
 	},
+	"round": {
+		Args:          []parse.ReturnType{parse.TypeVariantSet},
+		VariantReturn: true,
+		F:             round,
+	},
+	"ceil": {
+		Args:          []parse.ReturnType{parse.TypeVariantSet},
+		VariantReturn: true,
+		F:             ceil,
+	},
+	"floor": {
+		Args:          []parse.ReturnType{parse.TypeVariantSet},
+		VariantReturn: true,
+		F:             floor,
+	},
 }
 
 // abs returns the absolute value for each result in NumberSet, SeriesSet, or Scalar
@@ -253,3 +268,42 @@ func perNullableFloat(e *State, val Value, floatF func(x *float64) *float64) (Va
 
 	return newVal, nil
 }
+
+// round returns the rounded value for each result in NumberSet, SeriesSet, or Scalar
+func round(e *State, varSet Results) (Results, error) {
+	newRes := Results{}
+	for _, res := range varSet.Values {
+		newVal, err := perFloat(e, res, math.Round)
+		if err != nil {
+			return newRes, err
+		}
+		newRes.Values = append(newRes.Values, newVal)
+	}
+	return newRes, nil
+}
+
+// ceil returns the rounded up value for each result in NumberSet, SeriesSet, or Scalar
+func ceil(e *State, varSet Results) (Results, error) {
+	newRes := Results{}
+	for _, res := range varSet.Values {
+		newVal, err := perFloat(e, res, math.Ceil)
+		if err != nil {
+			return newRes, err
+		}
+		newRes.Values = append(newRes.Values, newVal)
+	}
+	return newRes, nil
+}
+
+// floor returns the rounded down value for each result in NumberSet, SeriesSet, or Scalar
+func floor(e *State, varSet Results) (Results, error) {
+	newRes := Results{}
+	for _, res := range varSet.Values {
+		newVal, err := perFloat(e, res, math.Floor)
+		if err != nil {
+			return newRes, err
+		}
+		newRes.Values = append(newRes.Values, newVal)
+	}
+	return newRes, nil
+}

pkg/expr/mathexp/reduce.go

@@ -69,6 +69,17 @@ func Count(fv *Float64Field) *float64 {
 	return &f
 }
 
+func Last(fv *Float64Field) *float64 {
+	var f float64
+	if fv.Len() == 0 {
+		f = math.NaN()
+		return &f
+	}
+	v := fv.GetValue(fv.Len() - 1)
+	f = *v
+	return &f
+}
+
 // Reduce turns the Series into a Number based on the given reduction function
 func (s Series) Reduce(refID, rFunc string) (Number, error) {
 	var l data.Labels
@@ -90,6 +101,8 @@ func (s Series) Reduce(refID, rFunc string) (Number, error) {
 		f = Max(&floatField)
 	case "count":
 		f = Count(&floatField)
+	case "last":
+		f = Last(&floatField)
 	default:
 		return number, fmt.Errorf("reduction %v not implemented", rFunc)
 	}

pkg/expr/mathexp/reduce_test.go

@@ -214,6 +214,19 @@ func TestSeriesReduce(t *testing.T) {
 				},
 			},
 		},
+		{
+			name:        "last empty series",
+			red:         "last",
+			varToReduce: "A",
+			vars:        seriesEmpty,
+			errIs:       require.NoError,
+			resultsIs:   require.Equal,
+			results: Results{
+				[]Value{
+					makeNumber("", nil, NaN),
+				},
+			},
+		},
 	}
 
 	for _, tt := range tests {