Dataset file formats

A FileFormat holds information about how to read and parse the files included in a Dataset. There are subclasses corresponding to the supported file formats (ParquetFileFormat and IpcFileFormat).

Factory

FileFormat$create() takes the following arguments:

• format: A string identifier of the file format. Currently supported values:

  • "parquet"

  • "ipc"/"arrow"/"feather", all aliases for each other; for Feather, note that only version 2 files are supported

  • "csv"/"text", aliases for the same thing (because comma is the default delimiter for text files

  • "tsv", equivalent to passing format = "text", delimiter = "\t"

• ...: Additional format-specific options

  format = "parquet":

  • dict_columns: Names of columns which should be read as dictionaries.

  • Any Parquet options from FragmentScanOptions.

  format = "text": see CsvParseOptions. Note that you can specify them either with the Arrow C++ library naming ("delimiter", "quoting", etc.) or the readr-style naming used in read_csv_arrow() ("delim", "quote", etc.). Not all readr options are currently supported; please file an issue if you encounter one that arrow should support. Also, the following options are supported. From CsvReadOptions:

  • skip_rows

  • column_names. Note that if a Schema is specified, column_names must match those specified in the schema.

  • autogenerate_column_names From CsvFragmentScanOptions (these values can be overridden at scan time):

  • convert_options: a CsvConvertOptions

  • block_size

It returns the appropriate subclass of FileFormat (e.g. ParquetFileFormat)

Examples

## Semi-colon delimited files
# Set up directory for examples
tf <- tempfile()
dir.create(tf)
on.exit(unlink(tf))
write.table(mtcars, file.path(tf, "file1.txt"), sep = ";", row.names = FALSE)

# Create FileFormat object
format <- FileFormat$create(format = "text", delimiter = ";")

open_dataset(tf, format = format)
#> FileSystemDataset with 1 csv file
#> 11 columns
#> mpg: double
#> cyl: int64
#> disp: double
#> hp: int64
#> drat: double
#> wt: double
#> qsec: double
#> vs: int64
#> am: int64
#> gear: int64
#> carb: int64