ParquetFileReader {arrow}

ParquetFileReader class

Description

This class enables you to interact with Parquet files.

Factory

The ParquetFileReader$create() factory method instantiates the object and takes the following arguments:

• file A character file name, raw vector, or Arrow file connection object (e.g. RandomAccessFile).

• props Optional ParquetArrowReaderProperties

• mmap Logical: whether to memory-map the file (default TRUE)

• reader_props Optional ParquetReaderProperties

• ... Additional arguments, currently ignored

Methods

• ⁠$ReadTable(column_indices)⁠: get an arrow::Table from the file. The optional ⁠column_indices=⁠ argument is a 0-based integer vector indicating which columns to retain.

• ⁠$ReadRowGroup(i, column_indices)⁠: get an arrow::Table by reading the ith row group (0-based). The optional ⁠column_indices=⁠ argument is a 0-based integer vector indicating which columns to retain.

• ⁠$ReadRowGroups(row_groups, column_indices)⁠: get an arrow::Table by reading several row groups (0-based integers). The optional ⁠column_indices=⁠ argument is a 0-based integer vector indicating which columns to retain.

• ⁠$GetSchema()⁠: get the arrow::Schema of the data in the file

• ⁠$ReadColumn(i)⁠: read the ith column (0-based) as a ChunkedArray.

Active bindings

• ⁠$num_rows⁠: number of rows.

• ⁠$num_columns⁠: number of columns.

• ⁠$num_row_groups⁠: number of row groups.

Examples

f <- system.file("v0.7.1.parquet", package = "arrow")
pq <- ParquetFileReader$create(f)
pq$GetSchema()
if (codec_is_available("snappy")) {
  # This file has compressed data columns
  tab <- pq$ReadTable()
  tab$schema
}