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ENH: DtypeWarning message enhancement #58174

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Closed
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VelizarVESSELINOV opened this issue Apr 7, 2024 · 2 comments · Fixed by #58250
Closed
1 of 3 tasks

ENH: DtypeWarning message enhancement #58174

VelizarVESSELINOV opened this issue Apr 7, 2024 · 2 comments · Fixed by #58250
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Enhancement IO CSV read_csv, to_csv Warnings Warnings that appear or should be added to pandas

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@VelizarVESSELINOV
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Feature Type

  • Adding new functionality to pandas

  • Changing existing functionality in pandas

  • Removing existing functionality in pandas

Problem Description

The current DtypeWarning message:
DtypeWarning: Columns (15,19) have mixed types. Specify dtype option on import or set low_memory=False.

Having a column name more than a column number would make sense.

Preferred warning message:

  1. DtypeWarning: Columns (15: Comment, 19: Description) have mixed types. Specify dtype option on import or set low_memory=False.
  2. DtypeWarning: Columns (15, 19) have mixed types. Specify dtype option ({'Comment': str, 'Description': str}) on import or set low_memory=False.

So the next user action can be easy:

read_csv(..., dtype={"Comment": str, "Description": str})

Feature Description

Current code:

def _concatenate_chunks(chunks: list[dict[int, ArrayLike]]) -> dict:
    """
    Concatenate chunks of data read with low_memory=True.

    The tricky part is handling Categoricals, where different chunks
    may have different inferred categories.
    """
    names = list(chunks[0].keys())
    warning_columns = []

    result: dict = {}
    for name in names:
        arrs = [chunk.pop(name) for chunk in chunks]
        # Check each arr for consistent types.
        dtypes = {a.dtype for a in arrs}
        non_cat_dtypes = {x for x in dtypes if not isinstance(x, CategoricalDtype)}

        dtype = dtypes.pop()
        if isinstance(dtype, CategoricalDtype):
            result[name] = union_categoricals(arrs, sort_categories=False)
        else:
            result[name] = concat_compat(arrs)
            if len(non_cat_dtypes) > 1 and result[name].dtype == np.dtype(object):
                warning_columns.append(str(name))

    if warning_columns:
        warning_names = ",".join(warning_columns)
        warning_message = " ".join(
            [
                f"Columns ({warning_names}) have mixed types. "
                f"Specify dtype option on import or set low_memory=False."
            ]
        )
        warnings.warn(warning_message, DtypeWarning, stacklevel=find_stack_level())
    return result
    ```

### Alternative Solutions

Replace columns number with column names

### Additional Context

_No response_
@VelizarVESSELINOV VelizarVESSELINOV added Enhancement Needs Triage Issue that has not been reviewed by a pandas team member labels Apr 7, 2024
@rhshadrach rhshadrach added IO CSV read_csv, to_csv Warnings Warnings that appear or should be added to pandas and removed Needs Triage Issue that has not been reviewed by a pandas team member labels Apr 8, 2024
@rhshadrach
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2. Specify dtype option ({'Comment': str, 'Description': str}) on import or set low_memory=False.

I don't think we should do this because column names can be duplicated. I'm okay with option 1.

@abeltavares
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take

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