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|
package dataset
import (
"context"
"errors"
"fmt"
"iter"
"path/filepath"
"slices"
"github.com/apache/arrow-go/v18/arrow"
"github.com/apache/arrow-go/v18/arrow/array"
"github.com/apache/arrow-go/v18/arrow/memory"
"github.com/apache/arrow-go/v18/parquet/file"
"github.com/apache/arrow-go/v18/parquet/pqarrow"
)
type Reader struct {
shards []string
batchSize int64
err error
}
func NewReader(name string) (*Reader, error) {
var shards []string
if matches, err := filepath.Glob(filepath.Join(name, "*.parquet")); err != nil {
return nil, err
} else {
shards = matches
}
if len(shards) == 0 {
return nil, fmt.Errorf("no parquet files in %q", name)
}
slices.Sort(shards)
r := &Reader{
shards: shards,
batchSize: 1024,
}
return r, nil
}
func (r *Reader) Err() error {
return r.err
}
func (r *Reader) Texts(column string) iter.Seq[string] {
return func(yield func(string) bool) {
for _, name := range r.shards {
err := read(name, column, r.batchSize, yield)
if errors.Is(err, stop) {
return
}
if err != nil {
r.err = err
return
}
}
}
}
var stop = errors.New("stop")
func read(name, column string, batchSize int64, yield func(string) bool) error {
var reader *file.Reader
if r, err := file.OpenParquetFile(name, false); err != nil {
return err
} else {
reader = r
defer reader.Close()
}
var arrowReader *pqarrow.FileReader
if r, err := pqarrow.NewFileReader(reader, pqarrow.ArrowReadProperties{BatchSize: batchSize}, memory.DefaultAllocator); err != nil {
return err
} else {
arrowReader = r
}
var schema *arrow.Schema
if s, err := arrowReader.Schema(); err != nil {
return err
} else {
schema = s
}
idxs := schema.FieldIndices(column)
if len(idxs) == 0 {
return errors.New("unknown column")
}
var recordReader pqarrow.RecordReader
if r, err := arrowReader.GetRecordReader(context.TODO(), []int{idxs[0]}, nil); err != nil {
return err
} else {
recordReader = r
defer recordReader.Release()
}
for recordReader.Next() {
record := recordReader.RecordBatch()
text, ok := record.Column(0).(*array.String)
if !ok {
return fmt.Errorf("unexpected column type")
}
for i := range int(record.NumRows()) {
if !text.IsValid(i) {
continue
}
if !yield(text.Value(i)) {
return stop
}
}
}
return nil
}
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