NEWS.md
In nanoparquet: Read and Write 'Parquet' Files

nanoparquet 0.4.2

write_parquet() now does not fail when writing files with a zero-length first page (#122).
read_parquet() can now read Parquet files that do not contain the dictionary page offset in their metadata. Polars creates such files (#132).

nanoparquet 0.4.1

write_parquet() now correctly converts double Date columns to integer columns (@eitsupi, #116).
read_parquet() now correctly reads FLOAT columns from files with multiple row groups.
read_parquet() now correctly reads Parquet files that have column chunks with both dictionary encoded and not dictionary encoded pages (#110).

nanoparquet 0.4.0

API changes:
parquet_schema() is now called read_parquet_schema(). The new parquet_schema() function falls back to read_parquet_schema() if it is called with a single string argument, with a warning.
parquet_info() is now called read_parquet_info(). parquet_info( still works for now, with a warning.
parquet_metadata() is now called read_parquet_metadata(). parquet_metadata() still works, with a warning.
parquet_column_types() is now deprecated, and issues a warning. Use read_parquet_schema() or the new infer_parquet_schema() function instead.
Other improvements:
The new parquet_schema() function creates a Parquet schema from scratch. You can use this schema as the new schema argument of write_parquet(), to specify how the columns of a data frame should be mapped to Parquet types.
New append_parquet() function to append a data frame to an existing Parquet file.
New col_select argument for read_parquet() to read a subset of columns from a Parquet file.
write_parquet() can now write multiple row groups. By default it puts at most 10 million rows into a single row group. You can choose the row groups manually with the row_groups argument.
write_parquet() now writes minimum and maximum values per row group for most types. See ?parquet_options() for turning this off. It also writes out the number of non-missing values.
Newly supported type conversions in write_parquet() via the schema argument:
- integer to INT64,
- integer to INT96,
- double to INT96,
- double to FLOAT,
- character to BYTE_ARRAY,
- character to FIXED_LEN_BYTE_ARRAY,
- character to ENUM,
- factor to ENUM.
- integer to DECIMAL, INT32,
- integer to DECIMAL, INT64,
- double to DECIMAL, INT32,
- double to DECIMAL, INT64,
- integer to INT(8, *), INT(16, *), INT(32, signed),
- double to INT(*, *),
- character to UUID,
- double to FLOAT16,
- list of raw vectors to BYTE_ARRAY,
- list of raw vectors to FIXED_LEN_BYTE_ARRAY.
write_parquet() can now write version 2 data pages. The default is still version 1, but it might change in the future.
write_parquet(file = ":raw:") now works correctly for larger data frames (#77).
New compression_level option to select the compression level manually. See ?parquet_options for details. (#91).
read_parquet() can now read from an R connection (#71).
read_parquet() now reads DECIMAL values correctly from INT32 and INT64 columns if their scale is not zero.
read_parquet() now reads JSON columns as character vectors, as documented.
read_parquet() now reads the FLOAT16 logical type as a real (double) vector.
The class argument of parquet_options() and the nanoparquet.class option now work again (#104).

nanoparquet 0.3.1

This version fixes a write_parquet() crash (#73).

nanoparquet 0.3.0

read_parquet() type mapping changes:
The STRING logical type and the UTF8 converted type are still read as a character vector, but BYTE_ARRAY types without a converted or logical types are not any more, and are read as a list of raw vectors. Missing values are indicated as NULL values.
The DECIMAL converted type is read as a REALSXP now, even if its type is FIXED_LEN_BYTE_ARRAY. (Not just if it is BYTE_ARRAY).
The UUID logical type is now read as a character vector, formatted as 00112233-4455-6677-8899-aabbccddeeff.
BYTE_ARRAY and FIXED_LEN_BYTE_ARRAY types without logical or converted types; or with unsupported ones: FLOAT16, INTERVAL; are now read into a list of raw vectors. Missing values are denoted by NULL.
write_parquet() now automatically uses dictionary encoding for columns that have many repeated values. Only the first 10k rows are used to decide if dictionary will be used or not. Similarly, logical columns are written in RLE encoding if they contain runs of repeated values. NA values are ignored when selecting the encoding (#18).
write_parquet() can now write a data frame to a memory buffer, returned as a raw vector, if the special ":raw:" filename is used (#31).
read_parquet() can now read Parquet files with V2 data pages (#37).
Both read_parquet() and write_parquet() now support GZIP and ZSTD compressed Parquet files.
read_parquet() now supports the RLE encoding for BOOLEAN columns and also supports the DELTA_BINARY_PACKED, DELTA_LENGTH_BYTE_ARRAY, DELTA_BYTE_ARRAY and BYTE_STREAM_SPLIT encodings.
The parquet_columns() function is now called parquet_column_types() and it can now map the column types of a data frame to Parquet types.
parquet_info(), parquet_metadata() and parquet_column_types() now work if the created_by metadata field is unset.
New parquet_options() function that you can use to set nanoparquet options for a single read_parquet() or write_parquet() call.

nanoparquet 0.2.0

First release on CRAN. It contains the Parquet reader from https://github.com/hannes/miniparquet, a Parquet writer, functions to read Parquet metadata, and many improvements.