Rename to percentile.

ext/stats/TODO.md

@@ -41,8 +41,6 @@ https://sqlite.org/lang_aggfunc.html
 - [X] `RANK() OVER window`
 - [X] `DENSE_RANK() OVER window`
 - [X] `PERCENT_RANK() OVER window`
-- [ ] `PERCENTILE_CONT(percentile) OVER window`
-- [ ] `PERCENTILE_DISC(percentile) OVER window`
 
 https://sqlite.org/windowfunctions.html#builtins
 
@@ -54,7 +52,5 @@ https://sqlite.org/windowfunctions.html#builtins
 ## Additional aggregates
 
 - [X] `MEDIAN(expression)`
-- [X] `QUANTILE_CONT(expression, quantile)`
-- [X] `QUANTILE_DISC(expression, quantile)`
-
-https://duckdb.org/docs/sql/aggregates.html
+- [X] `PERCENTILE_CONT(expression, fraction)`
+- [X] `PERCENTILE_DISC(expression, fraction)`

ext/stats/percentile.go

@@ -13,21 +13,21 @@ import (
 
 const (
 	median = iota
-	quant_cont
-	quant_disc
+	percentile_cont
+	percentile_disc
 )
 
-func newQuantile(kind int) func() sqlite3.AggregateFunction {
-	return func() sqlite3.AggregateFunction { return &quantile{kind: kind} }
+func newPercentile(kind int) func() sqlite3.AggregateFunction {
+	return func() sqlite3.AggregateFunction { return &percentile{kind: kind} }
 }
 
-type quantile struct {
+type percentile struct {
 	nums []float64
 	arg1 []byte
 	kind int
 }
 
-func (q *quantile) Step(ctx sqlite3.Context, arg ...sqlite3.Value) {
+func (q *percentile) Step(ctx sqlite3.Context, arg ...sqlite3.Value) {
 	if a := arg[0]; a.NumericType() != sqlite3.NULL {
 		q.nums = append(q.nums, a.Float())
 	}
@@ -36,7 +36,12 @@ func (q *quantile) Step(ctx sqlite3.Context, arg ...sqlite3.Value) {
 	}
 }
 
-func (q *quantile) Value(ctx sqlite3.Context) {
+func (q *percentile) Inverse(ctx sqlite3.Context, arg ...sqlite3.Value) {
+	// Implementing inverse allows certain queries that don't really need it to succeed.
+	ctx.ResultError(util.ErrorString("percentile: may not be used as a window function"))
+}
+
+func (q *percentile) Value(ctx sqlite3.Context) {
 	if len(q.nums) == 0 {
 		return
 	}
@@ -47,21 +52,21 @@ func (q *quantile) Value(ctx sqlite3.Context) {
 		floats []float64
 	)
 	if q.kind == median {
-		float, err = getQuantile(q.nums, 0.5, false)
+		float, err = getPercentile(q.nums, 0.5, false)
 		ctx.ResultFloat(float)
 	} else if err = json.Unmarshal(q.arg1, &float); err == nil {
-		float, err = getQuantile(q.nums, float, q.kind == quant_disc)
+		float, err = getPercentile(q.nums, float, q.kind == percentile_disc)
 		ctx.ResultFloat(float)
 	} else if err = json.Unmarshal(q.arg1, &floats); err == nil {
-		err = getQuantiles(q.nums, floats, q.kind == quant_disc)
+		err = getPercentiles(q.nums, floats, q.kind == percentile_disc)
 		ctx.ResultJSON(floats)
 	}
 	if err != nil {
-		ctx.ResultError(fmt.Errorf("quantile: %w", err))
+		ctx.ResultError(fmt.Errorf("percentile: %w", err))
 	}
 }
 
-func getQuantile(nums []float64, pos float64, disc bool) (float64, error) {
+func getPercentile(nums []float64, pos float64, disc bool) (float64, error) {
 	if pos < 0 || pos > 1 {
 		return 0, util.ErrorString("invalid pos")
 	}
@@ -77,9 +82,9 @@ func getQuantile(nums []float64, pos float64, disc bool) (float64, error) {
 	return math.FMA(f, m1, -math.FMA(f, m0, -m0)), nil
 }
 
-func getQuantiles(nums []float64, pos []float64, disc bool) error {
+func getPercentiles(nums []float64, pos []float64, disc bool) error {
 	for i := range pos {
-		v, err := getQuantile(nums, pos[i], disc)
+		v, err := getPercentile(nums, pos[i], disc)
 		if err != nil {
 			return err
 		}

ext/stats/percentile_test.go

@@ -10,7 +10,7 @@ import (
 	_ "github.com/ncruces/go-sqlite3/internal/testcfg"
 )
 
-func TestRegister_quantile(t *testing.T) {
+func TestRegister_percentile(t *testing.T) {
 	t.Parallel()
 
 	db, err := sqlite3.Open(":memory:")
@@ -34,8 +34,8 @@ func TestRegister_quantile(t *testing.T) {
 	stmt, _, err := db.Prepare(`
 		SELECT
 			median(x),
-			quantile_disc(x, 0.5),
-			quantile_cont(x, '[0.25, 0.5, 0.75]')
+			percentile_disc(x, 0.5),
+			percentile_cont(x, '[0.25, 0.5, 0.75]')
 		FROM data`)
 	if err != nil {
 		t.Fatal(err)
@@ -60,8 +60,8 @@ func TestRegister_quantile(t *testing.T) {
 	stmt, _, err = db.Prepare(`
 		SELECT
 			median(x),
-			quantile_disc(x, 0.5),
-			quantile_cont(x, '[0.25, 0.5, 0.75]')
+			percentile_disc(x, 0.5),
+			percentile_cont(x, '[0.25, 0.5, 0.75]')
 		FROM data
 		WHERE x < 5`)
 	if err != nil {
@@ -87,8 +87,8 @@ func TestRegister_quantile(t *testing.T) {
 	stmt, _, err = db.Prepare(`
 		SELECT
 			median(x),
-			quantile_disc(x, 0.5),
-			quantile_cont(x, '[0.25, 0.5, 0.75]')
+			percentile_disc(x, 0.5),
+			percentile_cont(x, '[0.25, 0.5, 0.75]')
 		FROM data
 		WHERE x < 0`)
 	if err != nil {
@@ -109,10 +109,10 @@ func TestRegister_quantile(t *testing.T) {
 
 	stmt, _, err = db.Prepare(`
 		SELECT
-			quantile_disc(x, -2),
-			quantile_cont(x, +2),
-			quantile_cont(x, ''),
-			quantile_cont(x, '[100]')
+			percentile_disc(x, -2),
+			percentile_cont(x, +2),
+			percentile_cont(x, ''),
+			percentile_cont(x, '[100]')
 		FROM data`)
 	if err != nil {
 		t.Fatal(err)

ext/stats/stats.go

@@ -18,8 +18,8 @@
 //   - 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
-//   - quantile_disc: discrete quantile
-//   - quantile_cont: continuous quantile
+//   - percentile_disc: discrete percentile
+//   - percentile_cont: continuous percentile
 //   - median: median value
 //   - every: boolean and
 //   - some: boolean or
@@ -37,12 +37,11 @@
 //   - percent_rank: relative rank of the row
 //   - cume_dist: cumulative distribution
 //
-// See: [ANSI SQL Aggregate Functions], [DuckDB Aggregate Functions]
+// See: [ANSI SQL Aggregate Functions]
 //
 // [Built-in Aggregate Functions]: https://sqlite.org/lang_aggfunc.html
 // [Built-in Window Functions]: https://sqlite.org/windowfunctions.html#builtins
 // [ANSI SQL Aggregate Functions]: https://www.oreilly.com/library/view/sql-in-a/9780596155322/ch04s02.html
-// [DuckDB Aggregate Functions]: https://duckdb.org/docs/sql/aggregates.html
 package stats
 
 import "github.com/ncruces/go-sqlite3"
@@ -67,9 +66,9 @@ func Register(db *sqlite3.Conn) {
 	db.CreateWindowFunction("regr_intercept", 2, flags, newCovariance(regr_intercept))
 	db.CreateWindowFunction("regr_count", 2, flags, newCovariance(regr_count))
 	db.CreateWindowFunction("regr_json", 2, flags, newCovariance(regr_json))
-	db.CreateWindowFunction("median", 1, flags, newQuantile(median))
-	db.CreateWindowFunction("quantile_cont", 2, flags, newQuantile(quant_cont))
-	db.CreateWindowFunction("quantile_disc", 2, flags, newQuantile(quant_disc))
+	db.CreateWindowFunction("median", 1, flags, newPercentile(median))
+	db.CreateWindowFunction("percentile_cont", 2, flags, newPercentile(percentile_cont))
+	db.CreateWindowFunction("percentile_disc", 2, flags, newPercentile(percentile_disc))
 	db.CreateWindowFunction("every", 1, flags, newBoolean(every))
 	db.CreateWindowFunction("some", 1, flags, newBoolean(some))
 }