a quicker empty check for group by

executor.go

@@ -2854,7 +2854,7 @@ TOP:
 	}
 	gbi.rows[i].id = rowID
 
-	if gbi.rows[i].row.Count() == 0 {
+	if gbi.rows[i].row.IsEmpty() {
 		goto TOP // I wanted to just call nextAtIdx again, but if a bunch of
 		// rows in a row were 0, I was worried we'd get into a stack
 		// overflow situation

row.go

@@ -16,6 +16,7 @@ package pilosa
 
 import (
 	"encoding/json"
+	"fmt"
 	"sort"
 
 	"github.com/pilosa/pilosa/roaring"
@@ -42,6 +43,20 @@ func NewRow(columns ...uint64) *Row {
 	return r
 }
 
+func (r *Row) IsEmpty() bool {
+	fmt.Println("what", len(r.segments))
+	if len(r.segments) == 0 {
+		return true
+	}
+	for i := range r.segments {
+		if r.segments[i].n > 0 {
+			return false
+		}
+
+	}
+	return true
+}
+
 // Merge merges data from other into r.
 func (r *Row) Merge(other *Row) {
 	var segments []rowSegment

row_test.go

@@ -111,3 +111,17 @@ func TestRow_Difference_Segment(t *testing.T) {
 		t.Fatalf("Test 2 Difference Results %v != expected %v\n", res.Columns(), exp)
 	}
 }
+
+func TestRow_IsEmpty(t *testing.T) {
+	r1 := pilosa.NewRow(1, ShardWidth)
+	r2 := pilosa.NewRow(0, 2*ShardWidth)
+	res := r2.Intersect(r1)
+
+	if r1.IsEmpty() {
+		t.Fatal("r1 Should Not Be Empty\n")
+	}
+	if !res.IsEmpty() {
+		t.Fatal("Result Should Be Empty\n")
+	}
+
+}