dask.dataframe.DataFrame.to_parquet

dask.dataframe.DataFrame.to_parquet

DataFrame.to_parquet(path, *args, **kwargs)[source]

Store Dask.dataframe to Parquet files

Parameters
dfdask.dataframe.DataFrame
pathstring or pathlib.Path

Destination directory for data. Prepend with protocol like s3:// or hdfs:// for remote data.

engine{‘auto’, ‘fastparquet’, ‘pyarrow’}, default ‘auto’

Parquet library to use. Options include: ‘auto’, ‘fastparquet’, and ‘pyarrow’. Defaults to ‘auto’, which uses fastparquet if it is installed, and falls back to pyarrow otherwise. Note that in the future this default ordering for ‘auto’ will switch, with pyarrow being used if it is installed, and falling back to fastparquet.

compressionstring or dict, default ‘snappy’

Either a string like "snappy" or a dictionary mapping column names to compressors like {"name": "gzip", "values": "snappy"}. Defaults to "snappy".

write_indexboolean, default True

Whether or not to write the index. Defaults to True.

appendbool, default False

If False (default), construct data-set from scratch. If True, add new row-group(s) to an existing data-set. In the latter case, the data-set must exist, and the schema must match the input data.

overwritebool, default False

Whether or not to remove the contents of path before writing the dataset. The default is False. If True, the specified path must correspond to a directory (but not the current working directory). This option cannot be set to True if append=True. NOTE: overwrite=True will remove the original data even if the current write operation fails. Use at your own risk.

ignore_divisionsbool, default False

If False (default) raises error when previous divisions overlap with the new appended divisions. Ignored if append=False.

partition_onlist, default None

Construct directory-based partitioning by splitting on these fields’ values. Each dask partition will result in one or more datafiles, there will be no global groupby.

storage_optionsdict, default None

Key/value pairs to be passed on to the file-system backend, if any.

custom_metadatadict, default None

Custom key/value metadata to include in all footer metadata (and in the global “_metadata” file, if applicable). Note that the custom metadata may not contain the reserved b”pandas” key.

write_metadata_filebool or None, default None

Whether to write the special _metadata file. If None (the default), a _metadata file will only be written if append=True and the dataset already has a _metadata file.

computebool, default True

If True (default) then the result is computed immediately. If False then a dask.dataframe.Scalar object is returned for future computation.

compute_kwargsdict, default True

Options to be passed in to the compute method

schemaSchema object, dict, or {“infer”, None}, default None

Global schema to use for the output dataset. Alternatively, a dict of pyarrow types can be specified (e.g. schema={“id”: pa.string()}). For this case, fields excluded from the dictionary will be inferred from _meta_nonempty. If “infer”, the first non-empty and non-null partition will be used to infer the type for “object” columns. If None (default), we let the backend infer the schema for each distinct output partition. If the partitions produce inconsistent schemas, pyarrow will throw an error when writing the shared _metadata file. Note that this argument is ignored by the “fastparquet” engine.

name_functioncallable, default None

Function to generate the filename for each output partition. The function should accept an integer (partition index) as input and return a string which will be used as the filename for the corresponding partition. Should preserve the lexicographic order of partitions. If not specified, files will created using the convention part.0.parquet, part.1.parquet, part.2.parquet, … and so on for each partition in the DataFrame.

**kwargs

Extra options to be passed on to the specific backend.

See also

read_parquet

Read parquet data to dask.dataframe

Notes

Each partition will be written to a separate file.

Examples

>>> df = dd.read_csv(...)  
>>> df.to_parquet('/path/to/output/', ...)

By default, files will be created in the specified output directory using the convention part.0.parquet, part.1.parquet, part.2.parquet, … and so on for each partition in the DataFrame. To customize the names of each file, you can use the name_function= keyword argument. The function passed to name_function will be used to generate the filename for each partition and should expect a partition’s index integer as input and return a string which will be used as the filename for the corresponding partition. Strings produced by name_function must preserve the order of their respective partition indices.

For example:

>>> name_function = lambda x: f"data-{x}.parquet"
>>> df.to_parquet('/path/to/output/', name_function=name_function)

will result in the following files being created:

/path/to/output/
    ├── data-0.parquet
    ├── data-1.parquet
    ├── data-2.parquet
    └── ...

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