milden6 commented on code in PR #429: URL: https://github.com/apache/arrow-go/pull/429#discussion_r2178170360
########## parquet/example_write_read_pq_test.go: ########## @@ -0,0 +1,183 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +package parquet_test + +import ( + "bytes" + "context" + "fmt" + "log" + + "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" + "github.com/apache/arrow-go/v18/parquet/compress" + "github.com/apache/arrow-go/v18/parquet/file" + "github.com/apache/arrow-go/v18/parquet/pqarrow" +) + +// In a real project, this should be tuned based on memory usage and performance needs +const batchSize = 2 + +// List of fields to read +var colNames = []string{"intField", "stringField", "listField"} + +func Example_writeReadParquet() { + // --- Phase 1: Writing parquet file --- + + // Create an in-memory buffer to simulate a file + // For writing real file to disk, use os.Create instead + buffer := &bytes.Buffer{} + + // Create a schema with three fields + fields := []arrow.Field{ + {Name: "intField", Type: arrow.PrimitiveTypes.Int32, Nullable: false}, + {Name: "stringField", Type: arrow.BinaryTypes.String, Nullable: false}, + {Name: "listField", Type: arrow.ListOf(arrow.PrimitiveTypes.Float32), Nullable: false}, + } + + schema := arrow.NewSchema(fields, nil) + + // Create parquet writer props with snappy compression + writerProps := parquet.NewWriterProperties( + parquet.WithCompression(compress.Codecs.Snappy), + ) + + // Create arrow writer props to store the schema in the parquet file + arrowWriterProps := pqarrow.NewArrowWriterProperties( + pqarrow.WithStoreSchema(), + ) + + // Create a parquet writer + writer, err := pqarrow.NewFileWriter(schema, buffer, writerProps, arrowWriterProps) + if err != nil { + log.Fatalf("Failed create parquet writer: %v", err) + } + + // Create a record builder + recordBuilder := array.NewRecordBuilder(memory.DefaultAllocator, schema) + + // Create a builder for each field + intFieldIdx := schema.FieldIndices("intField")[0] + stringFieldIdx := schema.FieldIndices("stringField")[0] + listFieldIdx := schema.FieldIndices("listField")[0] + + intFieldBuilder := recordBuilder.Field(intFieldIdx).(*array.Int32Builder) + stringFieldBuilder := recordBuilder.Field(stringFieldIdx).(*array.StringBuilder) + listFieldBuilder := recordBuilder.Field(listFieldIdx).(*array.ListBuilder) + + // Get the builder for the list's values (Float32) + fl32Builder := listFieldBuilder.ValueBuilder().(*array.Float32Builder) + + // Append values for each field + intFieldBuilder.AppendValues([]int32{38, 13, 53, 93, 66}, nil) + stringFieldBuilder.AppendValues([]string{"val1", "val2", "val3", "val4", "val5"}, nil) + + // Append five lists, each containing the same float32 values + for i := 0; i < 5; i++ { + listFieldBuilder.Append(true) + fl32Builder.AppendValues([]float32{1.0, 2.0, 4.0, 8.0}, nil) + } + + // Create a record + record := recordBuilder.NewRecord() + if err := writer.Write(record); err != nil { + log.Fatalf("Failed to write record: %v", err) + + } + + record.Release() + recordBuilder.Release() + + // IMPORTANT: Close the writer to finalize the file + if err := writer.Close(); err != nil { + log.Printf("Failed to close parquet writer: %v", err) + } + + // --- Phase 2: Reading parquet file --- + + // Create a Parquet reader from the in-memory buffer + // For reading real file from disk, use file.OpenParquetFile() instead + fileReader, err := file.NewParquetReader(bytes.NewReader(buffer.Bytes())) + if err != nil { + log.Fatalf("Failed to create parquet reader: %v", err) + } + defer func() { + if err := fileReader.Close(); err != nil { + log.Printf("Failed to close file reader: %v", err) + } + }() + + // Create arrow read props, specifying the batch size + arrowReadProps := pqarrow.ArrowReadProperties{BatchSize: batchSize} + + // Create an arrow reader for the parquet file + arrowReader, err := pqarrow.NewFileReader(fileReader, arrowReadProps, memory.DefaultAllocator) + if err != nil { + log.Fatalf("Failed to create arrow reader: %v", err) + } + + // Get the arrow schema from the file reader + schema, err = arrowReader.Schema() + if err != nil { + log.Fatalf("Failed to get schema: %v", err) + } + + // colIndices can be nil to read all columns. Here, we specify which columns to read + colIndices := make([]int, len(colNames)) + for idx := range colNames { + colIndices[idx] = schema.FieldIndices(colNames[idx])[0] + } + + // Get the current record from the reader + recordReader, err := arrowReader.GetRecordReader(context.TODO(), colIndices, nil) + if err != nil { + log.Fatalf("Failed to get record reader: %v", err) + } + defer recordReader.Release() + + for recordReader.Next() { + // Create a record + record := recordReader.Record() + record.Retain() + + // Get columns + intCol := record.Column(colIndices[0]).(*array.Int32) + stringCol := record.Column(colIndices[1]).(*array.String) + listCol := record.Column(colIndices[2]).(*array.List) + listValueCol := listCol.ListValues().(*array.Float32) + + // Iterate over the rows within the current record + for idx := range int(record.NumRows()) { + // For the list column, get the start and end offsets for the current row + start, end := listCol.ValueOffsets(idx) + + fmt.Printf("%d %s %v\n", intCol.Value(idx), stringCol.Value(idx), listValueCol.Float32Values()[start:end]) + } Review Comment: Are you sure? If I write it like this: ```go for recordReader.Next() { // Create a record record := recordReader.Record() fmt.Println(record) } ``` The output will be like this: ``` record: schema: fields: 3 - intField: type=int32 metadata: ["PARQUET:field_id": "-1"] - stringField: type=utf8 metadata: ["PARQUET:field_id": "-1"] - listField: type=list<element: float32, nullable> metadata: ["PARQUET:field_id": "-1"] rows: 2 col[0][intField]: [38 13] col[1][stringField]: ["val1" "val2"] col[2][listField]: [[1 2 4 8] [1 2 4 8]] record: schema: fields: 3 - intField: type=int32 metadata: ["PARQUET:field_id": "-1"] - stringField: type=utf8 metadata: ["PARQUET:field_id": "-1"] - listField: type=list<element: float32, nullable> metadata: ["PARQUET:field_id": "-1"] rows: 2 col[0][intField]: [53 93] col[1][stringField]: ["val3" "val4"] col[2][listField]: [[1 2 4 8] [1 2 4 8]] record: schema: fields: 3 - intField: type=int32 metadata: ["PARQUET:field_id": "-1"] - stringField: type=utf8 metadata: ["PARQUET:field_id": "-1"] - listField: type=list<element: float32, nullable> metadata: ["PARQUET:field_id": "-1"] rows: 1 col[0][intField]: [66] col[1][stringField]: ["val5"] col[2][listField]: [[1 2 4 8]] ``` Instead of: ``` 38 val1 [1 2 4 8] 13 val2 [1 2 4 8] 53 val3 [1 2 4 8] 93 val4 [1 2 4 8] 66 val5 [1 2 4 8] ``` Or did I misunderstand you? -- This is an automated message from the Apache Git Service. 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