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Hive

Scanning hive partitioned data

Polars supports scanning hive partitioned parquet and IPC datasets, with planned support for other formats in the future.

Hive partition parsing is enabled by default if scan_parquet receives a single directory path, otherwise it is disabled by default. This can be explicitly configured using the hive_partitioning parameter.

Scanning a hive directory

For this example the following directory structure is used:

┌───────────────────────────────────────────────────────┐
│ File path                                             │
╞═══════════════════════════════════════════════════════╡
│ docs/assets/data/hive/year=2023/month=11/data.parquet │
│ docs/assets/data/hive/year=2023/month=12/data.parquet │
│ docs/assets/data/hive/year=2024/month=01/data.parquet │
│ docs/assets/data/hive/year=2024/month=02/data.parquet │
└───────────────────────────────────────────────────────┘

Simply pass the directory to scan_parquet, and all files will be loaded with the hive parts in the path included in the output:

scan_parquet 

import polars as pl

df = pl.scan_parquet("docs/assets/data/hive/").collect()

with pl.Config(tbl_rows=99):
    print(df)


shape: (11, 3)
┌─────┬──────┬───────┐
│ x   ┆ year ┆ month │
│ --- ┆ ---  ┆ ---   │
│ i64 ┆ i64  ┆ i64   │
╞═════╪══════╪═══════╡
│ 1   ┆ 2023 ┆ 11    │
│ 2   ┆ 2023 ┆ 11    │
│ 3   ┆ 2023 ┆ 12    │
│ 4   ┆ 2023 ┆ 12    │
│ 5   ┆ 2023 ┆ 12    │
│ 6   ┆ 2024 ┆ 1     │
│ 7   ┆ 2024 ┆ 1     │
│ 8   ┆ 2024 ┆ 2     │
│ 9   ┆ 2024 ┆ 2     │
│ 10  ┆ 2024 ┆ 2     │
│ 11  ┆ 2024 ┆ 2     │
└─────┴──────┴───────┘

Handling mixed files

Passing a directory to scan_parquet may not work if there are files with different extensions in the directory.

For this example the following directory structure is used:

┌─────────────────────────────────────────────────────────────┐
│ File path                                                   │
╞═════════════════════════════════════════════════════════════╡
│ docs/assets/data/hive_mixed/description.txt                 │
│ docs/assets/data/hive_mixed/year=2023/month=11/data.parquet │
│ docs/assets/data/hive_mixed/year=2023/month=12/data.parquet │
│ docs/assets/data/hive_mixed/year=2024/month=01/data.parquet │
│ docs/assets/data/hive_mixed/year=2024/month=02/data.parquet │
└─────────────────────────────────────────────────────────────┘

scan_parquet 

from pathlib import Path

try:
    pl.scan_parquet("docs/assets/data/hive_mixed/").collect()
except Exception as e:
    print(e)

The above fails as description.txt is not a valid parquet file:

directory contained paths with different file extensions: \
                first path: docs/assets/data/hive_mixed/description.txt, second path: docs/assets/data/hive_mixed/year=2023/month=11/data.parquet. Please use a glob pattern to explicitly specify \
                which files to read (e.g. "dir/**/*", "dir/**/*.parquet")

In this situation, a glob pattern can be used to be more specific about which files to load. Note that hive_partitioning must explicitly set to True:

scan_parquet 

df = pl.scan_parquet(
    # Glob to match all files ending in `.parquet`
    "docs/assets/data/hive_mixed/**/*.parquet",
    hive_partitioning=True,
).collect()

with pl.Config(tbl_rows=99):
    print(df)


shape: (11, 3)
┌─────┬──────┬───────┐
│ x   ┆ year ┆ month │
│ --- ┆ ---  ┆ ---   │
│ i64 ┆ i64  ┆ i64   │
╞═════╪══════╪═══════╡
│ 1   ┆ 2023 ┆ 11    │
│ 2   ┆ 2023 ┆ 11    │
│ 3   ┆ 2023 ┆ 12    │
│ 4   ┆ 2023 ┆ 12    │
│ 5   ┆ 2023 ┆ 12    │
│ 6   ┆ 2024 ┆ 1     │
│ 7   ┆ 2024 ┆ 1     │
│ 8   ┆ 2024 ┆ 2     │
│ 9   ┆ 2024 ┆ 2     │
│ 10  ┆ 2024 ┆ 2     │
│ 11  ┆ 2024 ┆ 2     │
└─────┴──────┴───────┘

Scanning file paths with hive parts

hive_partitioning is not enabled by default for file paths:

scan_parquet 

df = pl.scan_parquet(
    [
        "docs/assets/data/hive/year=2024/month=01/data.parquet",
        "docs/assets/data/hive/year=2024/month=02/data.parquet",
    ],
).collect()

print(df)


shape: (6, 1)
┌─────┐
│ x   │
│ --- │
│ i64 │
╞═════╡
│ 6   │
│ 7   │
│ 8   │
│ 9   │
│ 10  │
│ 11  │
└─────┘

Pass hive_partitioning=True to enable hive partition parsing:

scan_parquet 

df = pl.scan_parquet(
    [
        "docs/assets/data/hive/year=2024/month=01/data.parquet",
        "docs/assets/data/hive/year=2024/month=02/data.parquet",
    ],
    hive_partitioning=True,
).collect()

print(df)


shape: (6, 3)
┌─────┬──────┬───────┐
│ x   ┆ year ┆ month │
│ --- ┆ ---  ┆ ---   │
│ i64 ┆ i64  ┆ i64   │
╞═════╪══════╪═══════╡
│ 6   ┆ 2024 ┆ 1     │
│ 7   ┆ 2024 ┆ 1     │
│ 8   ┆ 2024 ┆ 2     │
│ 9   ┆ 2024 ┆ 2     │
│ 10  ┆ 2024 ┆ 2     │
│ 11  ┆ 2024 ┆ 2     │
└─────┴──────┴───────┘

Writing hive partitioned data

Note: The following functionality is considered unstable, and is subject to change.

Polars supports writing hive partitioned parquet datasets, with planned support for other formats.

Example

For this example the following DataFrame is used:

df = pl.DataFrame({"a": [1, 1, 2, 2, 3], "b": [1, 1, 1, 2, 2], "c": 1})
print(df)

shape: (5, 3)
┌─────┬─────┬─────┐
│ a   ┆ b   ┆ c   │
│ --- ┆ --- ┆ --- │
│ i64 ┆ i64 ┆ i32 │
╞═════╪═════╪═════╡
│ 1   ┆ 1   ┆ 1   │
│ 1   ┆ 1   ┆ 1   │
│ 2   ┆ 1   ┆ 1   │
│ 2   ┆ 2   ┆ 1   │
│ 3   ┆ 2   ┆ 1   │
└─────┴─────┴─────┘

We will write it to a hive-partitioned parquet dataset, partitioned by the columns a and b:

write_parquet 

df.write_parquet("docs/assets/data/hive_write/", partition_by=["a", "b"])

The output is a hive partitioned parquet dataset with the following paths:

┌──────────────────────────────────────────────────────┐
│ File path                                            │
╞══════════════════════════════════════════════════════╡
│ docs/assets/data/hive_write/a=1/b=1/00000000.parquet │
│ docs/assets/data/hive_write/a=2/b=1/00000000.parquet │
│ docs/assets/data/hive_write/a=2/b=2/00000000.parquet │
│ docs/assets/data/hive_write/a=3/b=2/00000000.parquet │
└──────────────────────────────────────────────────────┘