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).
FileFormat$create() takes the following arguments:
format: A string identifier of the file format. Currently supported values:
"parquet"
"ipc"/"arrow"/"feather", all aliases for each other; for Feather, note that only version 2 files are supported
"csv"/"text", aliases for the same thing (because comma is the default delimiter for text files
"tsv", equivalent to passing format = "text", delimiter = "\t"
...: Additional format-specific options
`format = "parquet"``:
dict_columns: Names of columns which should be read as dictionaries.
Any Parquet options from FragmentScanOptions.
format = "text": see CsvParseOptions. Note that you can specify them either
with the Arrow C++ library naming ("delimiter", "quoting", etc.) or the
readr-style naming used in read_csv_arrow() ("delim", "quote", etc.).
Not all readr options are currently supported; please file an issue if
you encounter one that arrow should support. Also, the following options are
supported. From CsvReadOptions:
skip_rows
column_names. Note that if a Schema is specified, column_names must match those specified in the schema.
autogenerate_column_names
From CsvFragmentScanOptions (these values can be overridden at scan time):
convert_options: a CsvConvertOptions
block_size
It returns the appropriate subclass of FileFormat (e.g. ParquetFileFormat)
## Semi-colon delimited files
# Set up directory for examples
tf <- tempfile()
dir.create(tf)
on.exit(unlink(tf))
write.table(mtcars, file.path(tf, "file1.txt"), sep = ";", row.names = FALSE)
# Create FileFormat object
format <- FileFormat$create(format = "text", delimiter = ";")
open_dataset(tf, format = format)
#> FileSystemDataset with 1 csv file
#> mpg: double
#> cyl: int64
#> disp: double
#> hp: int64
#> drat: double
#> wt: double
#> qsec: double
#> vs: int64
#> am: int64
#> gear: int64
#> carb: int64