Panic in calling to_numpy on a concatted DataFrame

[rhshadrach-8451]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

pl.concat(
    [
        pl.DataFrame({"a": [1, 1, 2], "b": [2, 3, 4]}),
        pl.DataFrame({"a": [1, 1, 2], "b": [2, 3, 4]}),
    ]
).to_numpy()

Log output

thread 'polars-0' panicked at /home/runner/work/polars/polars/crates/polars-core/src/chunked_array/ndarray.rs:156:33:
source slice length (3) does not match destination slice length (6)
thread 'polars-0' panicked at /home/runner/work/polars/polars/crates/polars-core/src/chunked_array/ndarray.rs:156:33:
source slice length (3) does not match destination slice length (6)
---------------------------------------------------------------------------
PanicException                            Traceback (most recent call last)
/tmp/ipykernel_26173/271991162.py in ?()
      5     [
      6         pl.DataFrame({"a": [1, 1, 2], "b": [2, 3, 4]}),
      7         pl.DataFrame({"a": [1, 1, 2], "b": [2, 3, 4]}),
      8     ]
----> 9 ).to_numpy()

[snip]/python3.10/site-packages/polars/_utils/deprecation.py in ?(*args, **kwargs)
    223         @wraps(function)
    224         def wrapper(*args: P.args, **kwargs: P.kwargs) -> T:
    225             if len(args) > num_allowed_args:
    226                 issue_deprecation_warning(msg, version=version)
--> 227             return function(*args, **kwargs)

[snip]/python3.10/site-packages/polars/dataframe/frame.py in ?(self, structured, order, allow_copy, writable, use_pyarrow)
   1583             for idx, c in enumerate(self.columns):
   1584                 out[c] = arrays[idx]
   1585             return out
   1586 
-> 1587         return self._df.to_numpy(order, writable=writable, allow_copy=allow_copy)

PanicException: source slice length (3) does not match destination slice length (6)

Issue description

The code sample above worked in 0.20.26, but not in 0.20.27. May be due to #16288.

Expected behavior

Not raising.

Installed versions

--------Version info---------
Polars:               0.20.27
Index type:           UInt32
Platform:             Linux-5.10.102.1-microsoft-standard-WSL2-x86_64-with-glibc2.35
Python:               3.10.12 (main, Nov 20 2023, 15:14:05) [GCC 11.4.0]

----Optional dependencies----
adbc_driver_manager:  <not installed>
cloudpickle:          <not installed>
connectorx:           <not installed>
deltalake:            <not installed>
fastexcel:            0.10.4
fsspec:               2024.5.0
gevent:               <not installed>
hvplot:               0.10.0
matplotlib:           3.9.0
nest_asyncio:         1.6.0
numpy:                1.26.4
openpyxl:             <not installed>
pandas:               2.2.2
pyarrow:              16.1.0
pydantic:             2.7.1
pyiceberg:            <not installed>
pyxlsb:               <not installed>
sqlalchemy:           <not installed>
torch:                <not installed>
xlsx2csv:             0.8.2
xlsxwriter:           3.2.0

[cmdlineluser]

I think you are right about the cause, as it does work with rechunk enabled.

pl.concat(
    [
        pl.DataFrame({"a": [1, 1, 2], "b": [2, 3, 4]}),
        pl.DataFrame({"a": [1, 1, 2], "b": [2, 3, 4]}),
    ],
    rechunk = True
).to_numpy()

# array([[1, 2],
#        [1, 3],
#        [2, 4],
#        [1, 2],
#        [1, 3],
#        [2, 4]])

[yburke94]

This error is also hitting us since upgrading to 0.20.27

[ritchie46]

Fix coming up. I think I will do a patch.