Fix #215.

ext/stats/mode.go

@@ -0,0 +1,112 @@
+package stats
+
+import (
+	"unsafe"
+
+	"github.com/ncruces/go-sqlite3"
+)
+
+func newMode() sqlite3.AggregateFunction {
+	return &mode{}
+}
+
+type mode struct {
+	ints  counter[int64]
+	reals counter[float64]
+	texts counter[string]
+	blobs counter[string]
+}
+
+func (m mode) Value(ctx sqlite3.Context) {
+	var (
+		max = 0
+		typ = sqlite3.NULL
+		i64 int64
+		f64 float64
+		str string
+	)
+	for k, v := range m.ints {
+		if v > max || v == max && k < i64 {
+			typ = sqlite3.INTEGER
+			max = v
+			i64 = k
+		}
+	}
+	f64 = float64(i64)
+	for k, v := range m.reals {
+		if v > max || v == max && k < f64 {
+			typ = sqlite3.FLOAT
+			max = v
+			f64 = k
+		}
+	}
+	for k, v := range m.texts {
+		if v > max || v == max && typ == sqlite3.TEXT && k < str {
+			typ = sqlite3.TEXT
+			max = v
+			str = k
+		}
+	}
+	for k, v := range m.blobs {
+		if v > max || v == max && typ == sqlite3.BLOB && k < str {
+			typ = sqlite3.BLOB
+			max = v
+			str = k
+		}
+	}
+	switch typ {
+	case sqlite3.INTEGER:
+		ctx.ResultInt64(i64)
+	case sqlite3.FLOAT:
+		ctx.ResultFloat(f64)
+	case sqlite3.TEXT:
+		ctx.ResultText(str)
+	case sqlite3.BLOB:
+		ctx.ResultBlob(unsafe.Slice(unsafe.StringData(str), len(str)))
+	}
+}
+
+func (b *mode) Step(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	switch arg[0].Type() {
+	case sqlite3.INTEGER:
+		b.ints.add(arg[0].Int64())
+	case sqlite3.FLOAT:
+		b.reals.add(arg[0].Float())
+	case sqlite3.TEXT:
+		b.texts.add(arg[0].Text())
+	case sqlite3.BLOB:
+		b.blobs.add(string(arg[0].RawBlob()))
+	}
+}
+
+func (b *mode) Inverse(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	switch arg[0].Type() {
+	case sqlite3.INTEGER:
+		b.ints.del(arg[0].Int64())
+	case sqlite3.FLOAT:
+		b.reals.del(arg[0].Float())
+	case sqlite3.TEXT:
+		b.texts.del(arg[0].Text())
+	case sqlite3.BLOB:
+		b.blobs.del(string(arg[0].RawBlob()))
+	}
+}
+
+type counter[T comparable] map[T]int
+
+func (c *counter[T]) add(k T) {
+	if (*c) == nil {
+		(*c) = make(counter[T])
+	}
+	(*c)[k]++
+}
+
+func (c counter[T]) del(k T) {
+	switch n := c[k]; n {
+	default:
+		c[k] = n - 1
+	case 1:
+		delete(c, k)
+	case 0:
+	}
+}

ext/stats/mode_test.go

@@ -0,0 +1,85 @@
+package stats_test
+
+import (
+	"testing"
+
+	"github.com/ncruces/go-sqlite3"
+	_ "github.com/ncruces/go-sqlite3/embed"
+	_ "github.com/ncruces/go-sqlite3/internal/testcfg"
+)
+
+func TestRegister_mode(t *testing.T) {
+	t.Parallel()
+
+	db, err := sqlite3.Open(":memory:")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	stmt, _, err := db.Prepare(`SELECT mode(column1) FROM (VALUES (NULL), (1), (NULL), (2), (NULL), (3), (3))`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnInt(0); got != 3 {
+			t.Errorf("got %v, want 3", got)
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`SELECT mode(column1) FROM (VALUES (1), (1), (2), (2), (3))`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnInt(0); got != 1 {
+			t.Errorf("got %v, want 1", got)
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`SELECT mode(column1) FROM (VALUES (0.5), (1), (2.5), (2), (2.5))`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnFloat(0); got != 2.5 {
+			t.Errorf("got %v, want 2.5", got)
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`SELECT mode(column1) FROM (VALUES ('red'), ('green'), ('blue'), ('red'))`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnText(0); got != "red" {
+			t.Errorf("got %q, want red", got)
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`SELECT mode(column1) FROM (VALUES (X'cafebabe'), ('green'), ('blue'), (X'cafebabe'))`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if stmt.Step() {
+		if got := stmt.ColumnText(0); got != "\xca\xfe\xba\xbe" {
+			t.Errorf("got %q, want cafebabe", got)
+		}
+	}
+	stmt.Close()
+
+	stmt, _, err = db.Prepare(`
+		SELECT mode(column1) OVER (ROWS BETWEEN 1 PRECEDING AND 1 FOLLOWING)
+		FROM (VALUES (1), (1), (2.5), ('blue'), (X'cafebabe'), (1), (1))
+	`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for stmt.Step() {
+	}
+	stmt.Close()
+}

ext/stats/stats.go

@@ -18,9 +18,11 @@
 //   - regr_slope: slope of the least-squares-fit linear equation
 //   - regr_intercept: y-intercept of the least-squares-fit linear equation
 //   - regr_json: all regr stats in a JSON object
-//   - percentile_disc: discrete percentile
-//   - percentile_cont: continuous percentile
-//   - median: median value
+//   - percentile_disc: discrete quantile
+//   - percentile_cont: continuous quantile
+//   - percentile: continuous percentile
+//   - median: middle value
+//   - mode: most frequent value
 //   - every: boolean and
 //   - some: boolean or
 //
@@ -77,7 +79,8 @@ func Register(db *sqlite3.Conn) error {
 		db.CreateWindowFunction("percentile_cont", 2, order, newPercentile(percentile_cont)),
 		db.CreateWindowFunction("percentile_disc", 2, order, newPercentile(percentile_disc)),
 		db.CreateWindowFunction("every", 1, flags, newBoolean(every)),
-		db.CreateWindowFunction("some", 1, flags, newBoolean(some)))
+		db.CreateWindowFunction("some", 1, flags, newBoolean(some)),
+		db.CreateWindowFunction("mode", 1, order, newMode))
 }
 
 const (