Implement a COUNT ... BY aggregation operator.

This also removes the now obsolete scalar count() function and corrects the
expressions test naming (broken in
2202cd71c9 (L6R59))
so that the expression tests will actually run.

rules/ast/ast.go

@@ -82,6 +82,7 @@ const (
 	AVG
 	MIN
 	MAX
+	COUNT
 )
 
 // ----------------------------------------------------------------------------
@@ -317,8 +318,13 @@ func labelIntersection(metric1, metric2 model.Metric) model.Metric {
 func (node *VectorAggregation) groupedAggregationsToVector(aggregations map[string]*groupedAggregation, timestamp time.Time) Vector {
 	vector := Vector{}
 	for _, aggregation := range aggregations {
-		if node.aggrType == AVG {
+		switch node.aggrType {
+		case AVG:
 			aggregation.value = aggregation.value / model.SampleValue(aggregation.groupCount)
+		case COUNT:
+			aggregation.value = model.SampleValue(aggregation.groupCount)
+		default:
+			// For other aggregations, we already have the right value.
 		}
 		sample := model.Sample{
 			Metric:    aggregation.labels,
@@ -351,6 +357,10 @@ func (node *VectorAggregation) Eval(timestamp time.Time, view *viewAdapter) Vect
 				if groupedResult.value > sample.Value {
 					groupedResult.value = sample.Value
 				}
+			case COUNT:
+				groupedResult.groupCount++
+			default:
+				panic("Unknown aggregation type")
 			}
 		} else {
 			result[groupingKey] = &groupedAggregation{

rules/ast/functions.go

@@ -69,11 +69,6 @@ func timeImpl(timestamp time.Time, view *viewAdapter, args []Node) interface{} {
 	return model.SampleValue(time.Now().Unix())
 }
 
-// === count(vector VectorNode) model.SampleValue ===
-func countImpl(timestamp time.Time, view *viewAdapter, args []Node) interface{} {
-	return model.SampleValue(len(args[0].(VectorNode).Eval(timestamp, view)))
-}
-
 // === delta(matrix MatrixNode, isCounter ScalarNode) Vector ===
 func deltaImpl(timestamp time.Time, view *viewAdapter, args []Node) interface{} {
 	matrixNode := args[0].(MatrixNode)
@@ -253,12 +248,6 @@ func sampleVectorImpl(timestamp time.Time, view *viewAdapter, args []Node) inter
 }
 
 var functions = map[string]*Function{
-	"count": {
-		name:       "count",
-		argTypes:   []ExprType{VECTOR},
-		returnType: SCALAR,
-		callFn:     countImpl,
-	},
 	"delta": {
 		name:       "delta",
 		argTypes:   []ExprType{MATRIX, SCALAR},

rules/ast/printer.go

@@ -54,6 +54,7 @@ func (aggrType AggrType) String() string {
 		AVG:   "AVG",
 		MIN:   "MIN",
 		MAX:   "MAX",
+		COUNT: "COUNT",
 	}
 	return aggrTypeMap[aggrType]
 }

rules/helpers.go

@@ -59,6 +59,7 @@ func NewVectorAggregation(aggrTypeStr string, vector ast.Node, groupBy []model.L
 		"MAX":   ast.MAX,
 		"MIN":   ast.MIN,
 		"AVG":   ast.AVG,
+		"COUNT": ast.COUNT,
 	}
 	aggrType, ok := aggrTypes[aggrTypeStr]
 	if !ok {

rules/lexer.l

@@ -44,8 +44,8 @@ WITH|with                { return WITH }
 
 PERMANENT|permanent      { return PERMANENT }
 BY|by                    { return GROUP_OP }
-AVG|SUM|MAX|MIN          { yylval.str = yytext; return AGGR_OP }
+AVG|SUM|MAX|MIN|COUNT    { yylval.str = yytext; return AGGR_OP }
-avg|sum|max|min          { yylval.str = strings.ToUpper(yytext); return AGGR_OP }
+avg|sum|max|min|count    { yylval.str = strings.ToUpper(yytext); return AGGR_OP }
 \<|>|AND|OR|and|or       { yylval.str = strings.ToUpper(yytext); return CMP_OP }
 ==|!=|>=|<=              { yylval.str = yytext; return CMP_OP }
 [+\-]                    { yylval.str = yytext; return ADDITIVE_OP }

rules/lexer.l.go

@@ -380,7 +380,7 @@ var yyrules []yyrule = []yyrule{{regexp.MustCompile("[^\\n]"), nil, []yystartcon
 		return yyactionreturn{GROUP_OP, yyRT_USER_RETURN}
 	}
 	return yyactionreturn{0, yyRT_FALLTHROUGH}
-}}, {regexp.MustCompile("AVG|SUM|MAX|MIN"), nil, []yystartcondition{}, false, func() (yyar yyactionreturn) {
+}}, {regexp.MustCompile("AVG|SUM|MAX|MIN|COUNT"), nil, []yystartcondition{}, false, func() (yyar yyactionreturn) {
 	defer func() {
 		if r := recover(); r != nil {
 			if r != "yyREJECT" {
@@ -394,7 +394,7 @@ var yyrules []yyrule = []yyrule{{regexp.MustCompile("[^\\n]"), nil, []yystartcon
 		return yyactionreturn{AGGR_OP, yyRT_USER_RETURN}
 	}
 	return yyactionreturn{0, yyRT_FALLTHROUGH}
-}}, {regexp.MustCompile("avg|sum|max|min"), nil, []yystartcondition{}, false, func() (yyar yyactionreturn) {
+}}, {regexp.MustCompile("avg|sum|max|min|count"), nil, []yystartcondition{}, false, func() (yyar yyactionreturn) {
 	defer func() {
 		if r := recover(); r != nil {
 			if r != "yyREJECT" {
@@ -509,7 +509,6 @@ var yyrules []yyrule = []yyrule{{regexp.MustCompile("[^\\n]"), nil, []yystartcon
 		yylval.num = model.SampleValue(num)
 		return yyactionreturn{NUMBER, yyRT_USER_RETURN}
 	}
-
 	return yyactionreturn{0, yyRT_FALLTHROUGH}
 }}, {regexp.MustCompile("\\\"(\\\\[^\\n]|[^\\\\\"])*\\\""), nil, []yystartcondition{}, false, func() (yyar yyactionreturn) {
 	defer func() {

rules/rules_test.go

@@ -58,7 +58,7 @@ func newTestStorage(t test.Tester) (storage *metric.TieredStorage, closer test.C
 	return
 }
 
-func ExpressionTests(t *testing.T) {
+func TestExpressions(t *testing.T) {
 	// Labels in expected output need to be alphabetically sorted.
 	var expressionTests = []struct {
 		expr           string
@@ -81,6 +81,14 @@ func ExpressionTests(t *testing.T) {
 			},
 			fullRanges:     0,
 			intervalRanges: 8,
+		}, {
+			expr: "COUNT(http_requests) BY (job)",
+			output: []string{
+				"http_requests{job='api-server'} => 4 @[%v]",
+				"http_requests{job='app-server'} => 4 @[%v]",
+			},
+			fullRanges:     0,
+			intervalRanges: 8,
 		}, {
 			expr: "SUM(http_requests) BY (job, group)",
 			output: []string{
@@ -116,10 +124,10 @@ func ExpressionTests(t *testing.T) {
 			fullRanges:     0,
 			intervalRanges: 8,
 		}, {
-			expr: "SUM(http_requests) BY (job) - count(http_requests)",
+			expr: "SUM(http_requests) BY (job) - COUNT(http_requests) BY (job)",
 			output: []string{
-				"http_requests{job='api-server'} => 992 @[%v]",
+				"http_requests{job='api-server'} => 996 @[%v]",
-				"http_requests{job='app-server'} => 2592 @[%v]",
+				"http_requests{job='app-server'} => 2596 @[%v]",
 			},
 			fullRanges:     0,
 			intervalRanges: 8,