nanoparquet (version 0.4.2)

write_parquet: Write a data frame to a Parquet file

Description

Writes the contents of an R data frame into a Parquet file.

Usage

write_parquet(
  x,
  file,
  schema = NULL,
  compression = c("snappy", "gzip", "zstd", "uncompressed"),
  encoding = NULL,
  metadata = NULL,
  row_groups = NULL,
  options = parquet_options()
)

Value

NULL, unless file is ":raw:", in which case the Parquet file is returned as a raw vector.

Arguments

x

Data frame to write.

file

Path to the output file. If this is the string ":raw:", then the data frame is written to a memory buffer, and the memory buffer is returned as a raw vector.

schema

Parquet schema. Specify a schema to tweak the default nanoparquet R -> Parquet type mappings. Use parquet_schema() to create a schema that you can use here, or read_parquet_schema() to use the schema of a Parquet file.

compression

Compression algorithm to use. Currently "snappy" (the default), "gzip", "zstd", and "uncompressed" are supported.

encoding

Encoding to use. Possible values:

• If NULL, the appropriate encoding is selected automatically: RLE or PLAIN for BOOLEAN columns, RLE_DICTIONARY for other columns with many repeated values, and PLAIN otherwise.

• If It is a single (unnamed) character string, then it'll be used for all columns.

• If it is an unnamed character vector of encoding names of the same length as the number of columns in the data frame, then those encodings will be used for each column.

• If it is a named character vector, then the named must be unique and each name must match a column name, to specify the encoding of that column. The special empty name ("") applies to the rest of the columns. If there is no empty name, the rest of the columns will use the default encoding.

If NA_character_ is specified for a column, the default encoding is used for the column.

If a specified encoding is invalid for a certain column type, or nanoparquet does not implement it, write_parquet() throws an error.

Currently write_parquet() supports the following encodings:

• PLAIN for all column types,

• PLAIN_DICTIONARY and RLE_DICTIONARY for all column types,

• RLE for BOOLEAN columns.

See parquet-encodings for more about encodings.

metadata

Additional key-value metadata to add to the file. This must be a named character vector, or a data frame with columns character columns called key and value.

row_groups

Row groups of the Parquet file. If NULL, then the num_rows_per_row_group option is used from the options argument, see parquet_options(). Otherwise it must be an integer vector, specifying the starts of the row groups.

options

Nanoparquet options, see parquet_options().

Details

write_parquet() converts string columns to UTF-8 encoding by calling base::enc2utf8(). It does the same for factor levels.

See Also

read_parquet_metadata(), read_parquet().

Examples

if (FALSE) {
# add row names as a column, because `write_parquet()` ignores them.
mtcars2 <- cbind(name = rownames(mtcars), mtcars)
write_parquet(mtcars2, "mtcars.parquet")
}