made SelectRows public + modernized syntax

CHANGELOG.md

@@ -20,7 +20,7 @@ All notable changes to this project will be documented in this file.
   result := df.Filter("bad_column", "==", 1)
   ```
 
-- **`Head` and `Tail` panic on time columns** — The internal `slice()` function had no `TimeType` case, causing it to fall through to the error path on any DataFrame that contained a time column. Added the missing `case TimeType:` branch, consistent with the pattern already used in `selectRows()`.
+- **`Head` and `Tail` panic on time columns** — The internal `slice()` function had no `TimeType` case, causing it to fall through to the error path on any DataFrame that contained a time column. Added the missing `case TimeType:` branch, consistent with the pattern already used in `SelectRows()`.
 
 - **GroupBy key collisions on pipe characters** — Group keys were built by joining column values with `"|"`, meaning a value containing that character (e.g. `"a|b"`) would be indistinguishable from two separate values (`"a"` and `"b"`) in a multi-column group. Keys are now length-prefixed (`"3:foo"`) and separated by a null byte, making them unambiguous for all string content. The original values are stored directly on the group struct so no parsing of the key is needed when building the result.
 

README.md

@@ -2,7 +2,8 @@
 
 _Smooth, intelligent data processing for Go._
 
-Otters is a high-performance DataFrame library for Go, inspired by Pandas but designed for Go's strengths: type safety, performance, and simplicity.
+Otters is a high-performance DataFrame library for Go, inspired by Pandas but designed for Go's
+strengths: type safety, performance, and simplicity.
 
 [![Go Version](https://img.shields.io/badge/go-1.19+-blue.svg)](https://golang.org)
 [![Go Report Card](https://goreportcard.com/badge/github.com/datumbrain/otters)](https://goreportcard.com/report/github.com/datumbrain/otters)
@@ -180,7 +181,7 @@ df, err := otters.ReadCSVWithOptions("data.csv", otters.CSVOptions{
 })
 
 // From data
-df, err := otters.NewDataFrameFromMap(map[string]interface{}{
+df, err := otters.NewDataFrameFromMap(map[string]any{
     "name":   []string{"Alice", "Bob", "Carol"},
     "age":    []int64{25, 30, 35},
     "salary": []float64{50000, 60000, 70000},

csv.go

@@ -45,7 +45,7 @@ func ReadCSVWithOptions(filename string, options CSVOptions) (*DataFrame, error)
 }
 
 func skipRows(reader *csv.Reader, skipCount int, operation string) error {
-	for i := 0; i < skipCount; i++ {
+	for range skipCount {
 		if _, err := reader.Read(); err != nil {
 			if err == io.EOF {
 				return nil
@@ -112,7 +112,7 @@ func readCSVWithoutHeaders(reader *csv.Reader, options CSVOptions, operation str
 
 func generateHeaders(count int) []string {
 	headers := make([]string, count)
-	for i := 0; i < count; i++ {
+	for i := range count {
 		headers[i] = fmt.Sprintf("Column_%d", i)
 	}
 	return headers
@@ -137,7 +137,7 @@ func readDataRows(reader *csv.Reader, headers []string, options CSVOptions, oper
 		}
 
 		rows = append(rows, row)
-		rowCount++
+		rowCount += 1
 
 		if options.MaxRows > 0 && rowCount >= options.MaxRows {
 			break
@@ -181,7 +181,7 @@ func (df *DataFrame) WriteCSVWithOptions(filename string, options CSVOptions) er
 	}
 
 	// Write data rows
-	for i := 0; i < df.length; i++ {
+	for i := range df.length {
 		var row []string
 		for _, colName := range df.order {
 			value, err := df.columns[colName].Get(i)
@@ -289,7 +289,7 @@ func buildDataFrameFromRows(headers []string, rows [][]string) (*DataFrame, erro
 }
 
 // convertStringSliceToType converts a slice of strings to the specified type
-func convertStringSliceToType(values []string, targetType ColumnType) (interface{}, error) {
+func convertStringSliceToType(values []string, targetType ColumnType) (any, error) {
 	switch targetType {
 	case StringType:
 		// Return a copy to avoid external modification
@@ -367,7 +367,7 @@ func cleanHeader(header string) string {
 }
 
 // formatValueForCSV formats a value for CSV output
-func formatValueForCSV(value interface{}) string {
+func formatValueForCSV(value any) string {
 	switch v := value.(type) {
 	case string:
 		return v
@@ -479,7 +479,7 @@ func ValidateCSV(filename string) (*CSVInfo, error) {
 					info.Rows+1, info.Columns, len(row)))
 		}
 
-		info.Rows++
+		info.Rows += 1
 	}
 
 	return info, nil

csv_test.go

@@ -99,7 +99,7 @@ Bob,30`
 }
 
 func TestWriteCSVEdgeCases(t *testing.T) {
-	data := map[string]interface{}{
+	data := map[string]any{
 		"col1": []int64{1, 2, 3},
 		"col2": []string{"a", "b", "c"},
 	}
@@ -398,7 +398,7 @@ func TestCSV_WriteCSV_PropagatesDataFrameError(t *testing.T) {
 }
 
 func TestCSV_WriteCSVWithOptions_WritesFile(t *testing.T) {
-	data := map[string]interface{}{
+	data := map[string]any{
 		"col1": []int64{1, 2, 3},
 		"col2": []float64{1.1, 2.2, 3.3},
 		"col3": []bool{true, false, true},
@@ -420,7 +420,7 @@ func TestCSV_WriteCSVWithOptions_WritesFile(t *testing.T) {
 
 func TestCSV_WriteCSV_TimeColumn_WritesFile(t *testing.T) {
 	tm := time.Date(2023, 1, 1, 12, 30, 0, 0, time.UTC)
-	data := map[string]interface{}{
+	data := map[string]any{
 		"col1": []time.Time{tm, tm},
 	}
 	df, _ := NewDataFrameFromMap(data)

df.go

@@ -31,7 +31,7 @@ func NewDataFrameFromSeries(series ...*Series) (*DataFrame, error) {
 }
 
 // NewDataFrameFromMap creates a DataFrame from a map of column data
-func NewDataFrameFromMap(data map[string]interface{}) (*DataFrame, error) {
+func NewDataFrameFromMap(data map[string]any) (*DataFrame, error) {
 	if len(data) == 0 {
 		return NewDataFrame(), nil
 	}
@@ -157,7 +157,7 @@ func (df *DataFrame) Tail(n int) *DataFrame {
 }
 
 // Get returns the value at the specified row and column
-func (df *DataFrame) Get(row int, column string) (interface{}, error) {
+func (df *DataFrame) Get(row int, column string) (any, error) {
 	if df.err != nil {
 		return nil, df.err
 	}
@@ -174,7 +174,7 @@ func (df *DataFrame) Get(row int, column string) (interface{}, error) {
 }
 
 // Set updates the value at the specified row and column
-func (df *DataFrame) Set(row int, column string, value interface{}) error {
+func (df *DataFrame) Set(row int, column string, value any) error {
 	if df.err != nil {
 		return df.err
 	}
@@ -332,12 +332,9 @@ func (df *DataFrame) String() string {
 	sb.WriteString("\n")
 
 	// Write data (show first 10 rows max for display)
-	maxRows := df.length
-	if maxRows > 10 {
-		maxRows = 10
-	}
+	maxRows := min(df.length, 10)
 
-	for i := 0; i < maxRows; i++ {
+	for i := range maxRows {
 		var row []string
 		for _, colName := range df.order {
 			value, _ := df.columns[colName].Get(i)
@@ -348,7 +345,7 @@ func (df *DataFrame) String() string {
 	}
 
 	if df.length > 10 {
-		sb.WriteString(fmt.Sprintf("... (%d more rows)\n", df.length-10))
+		fmt.Fprintf(&sb, "... (%d more rows)\n", df.length-10)
 	}
 
 	return sb.String()
@@ -362,12 +359,12 @@ func (df *DataFrame) Info() string {
 
 	var sb strings.Builder
 	sb.WriteString("DataFrame Info:\n")
-	sb.WriteString(fmt.Sprintf("  Shape: (%d, %d)\n", df.length, len(df.columns)))
+	fmt.Fprintf(&sb, "  Shape: (%d, %d)\n", df.length, len(df.columns))
 	sb.WriteString("  Columns:\n")
 
 	for _, colName := range df.order {
 		series := df.columns[colName]
-		sb.WriteString(fmt.Sprintf("    %s: %s\n", colName, series.Type.String()))
+		fmt.Fprintf(&sb, "    %s: %s\n", colName, series.Type.String())
 	}
 
 	return sb.String()
@@ -394,7 +391,7 @@ func (df *DataFrame) slice(start, end int, operation string) *DataFrame {
 
 	for _, colName := range df.order {
 		series := df.columns[colName]
-		var newData interface{}
+		var newData any
 
 		// Slice the appropriate data type
 		switch series.Type {