ParquetFileReader class

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 ParquetReaderProperties

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

• ... 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

# \donttest{
f <- system.file("v0.7.1.parquet", package="arrow")
pq <- ParquetFileReader$create(f)
pq$GetSchema()
#> Schema
#> carat: double
#> cut: string
#> color: string
#> clarity: string
#> depth: double
#> table: double
#> price: int64
#> x: double
#> y: double
#> z: double
#> __index_level_0__: int64
#> 
#> See $metadata for additional Schema metadata
if (codec_is_available("snappy")) {
  # This file has compressed data columns
  tab <- pq$ReadTable()
  tab$schema
}
#> Schema
#> carat: double
#> cut: string
#> color: string
#> clarity: string
#> depth: double
#> table: double
#> price: int64
#> x: double
#> y: double
#> z: double
#> __index_level_0__: int64
#> 
#> See $metadata for additional Schema metadata
# }