ParquetFileReader class — ParquetFileReader • Arrow R Package

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()
#> 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