Maybe fix column selection

[martindurant]

@hombit , can you test, please? I fear this may be over reading bytes, but at least all the tests pass, including your specific case.

[hombit]

I'm looking into it. All examples from #1973 work now! Let me try running our CI in different repos vs this branch

[hombit]

Sorry, I think I messed up something. The test from the issue still fails:

uv venv venv
source venv/bin/activate
uv pip install git+https://github.com/martindurant/filesystem_spec@parquet-nested pyarrow

import random
import pyarrow as pa
import pyarrow.parquet as pq
from fsspec.parquet import open_parquet_file

def test(n, path):
    flat = pa.array([random.random() for _ in range(n)])
    nested = pa.array([{"a": random.random(), "b": random.random()} for _ in range(n)])
    table = pa.table({"flat": flat, "nested": nested})
    pq.write_table(table, path)
    with open_parquet_file(path, columns=["nested.a"], engine="pyarrow") as fh:
        _ = pq.read_table(fh)

# works for 10 rows
test(10, "/tmp/ten.parquet")

# fails for 100k rows
test(100_000, "100k.parquet")

OSError: Malformed levels. min: 2 max: 2 out of range.  Max Level: 1

[martindurant]

I added the test https://github.com/fsspec/filesystem_spec/pull/1979/files#diff-ff7fd767388891014a980915bb4fb6a84233cd96324d59e80ce9d2db18577791R208-R220 that is supposed to be identical. I wonder what the difference is.

[martindurant]

(sorry, this link:

filesystem_spec/fsspec/tests/test_parquet.py

Line 208 in 8ba3aae

def test_nested(n, tmpdir, engine):

)

[hombit]

Sorry, it was my mistake with the code: pq.read_table(fh) doesn't have columns=columns. It passes when I add it. I'm still testing with other repositories, give me some time

[hombit]

Could you please try with the files I shared in #1973? It still fails for me with double-nested columns (e.g. "spectrum.flux" is a list-array itself).

[hombit]

The test you introduced is a little bit different from the code in my original issue: you reuse the same a and b values for the nested column, which makes them very small on the disk because of encoding and compression.

If I change you test with either 1) {"a": random.random(), "b": random.random()}, or 2) pq.write_table(table, path, use_dictionary=False, compression=None), it fails with the same "Couldn't deserialize thrift" error.

Reproducible code

uv venv venv
source venv/bin/activate
uv pip install git+https://github.com/martindurant/filesystem_spec@parquet-nested pyarrow pandas

import os
import random

import pyarrow as pa
import pyarrow.parquet as pq
import pandas as pd
from fsspec.parquet import open_parquet_file

def test_nested(n, tmpdir, engine):
    path = os.path.join(str(tmpdir), "test.parquet")
    import pyarrow as pa
    flat = pa.array([random.random() for _ in range(n)])
    a = random.random()
    b = random.random()
    nested = pa.array([{"a": a, "b": b} for _ in range(n)])
    table = pa.table({"flat": flat, "nested": nested})
    pq.write_table(table, path, use_dictionary=False, compression=None)
    with open_parquet_file(path, columns=["nested.a"], engine=engine) as fh:
        col = pd.read_parquet(fh, engine=engine, columns=["nested.a"])
    name = "a" if engine == "pyarrow" else "nested.a"
    assert (col[name] == a).all()
test_nested(1_000_000, '/tmp', 'pyarrow')

Traceback (most recent call last):
  File "<python-input-1>", line 22, in <module>
    test_nested(1_000_000, '/tmp', 'pyarrow')
    ~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<python-input-1>", line 19, in test_nested
    col = pd.read_parquet(fh, engine=engine, columns=["nested.a"])
  File "/private/tmp/venv/lib/python3.14/site-packages/pandas/io/parquet.py", line 671, in read_parquet
    return impl.read(
           ~~~~~~~~~^
        path,
        ^^^^^
    ...<6 lines>...
        **kwargs,
        ^^^^^^^^^
    )
    ^
  File "/private/tmp/venv/lib/python3.14/site-packages/pandas/io/parquet.py", line 260, in read
    pa_table = self.api.parquet.read_table(
        path_or_handle,
    ...<3 lines>...
        **kwargs,
    )
  File "/private/tmp/venv/lib/python3.14/site-packages/pyarrow/parquet/core.py", line 1926, in read_table
    return dataset.read(columns=columns, use_threads=use_threads,
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                        use_pandas_metadata=use_pandas_metadata)
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/private/tmp/venv/lib/python3.14/site-packages/pyarrow/parquet/core.py", line 1552, in read
    table = self._dataset.to_table(
        columns=columns, filter=self._filter_expression,
        use_threads=use_threads
    )
  File "pyarrow/_dataset.pyx", line 589, in pyarrow._dataset.Dataset.to_table
  File "pyarrow/_dataset.pyx", line 3969, in pyarrow._dataset.Scanner.to_table
  File "pyarrow/error.pxi", line 155, in pyarrow.lib.pyarrow_internal_check_status
  File "pyarrow/error.pxi", line 92, in pyarrow.lib.check_status
OSError: Couldn't deserialize thrift: TProtocolException: Invalid data
Deserializing page header failed.