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DEPR: Make dtype="category" always imply ordered=False #61074

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mroeschke opened this issue Mar 7, 2025 · 2 comments · May be fixed by #61118
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DEPR: Make dtype="category" always imply ordered=False #61074

mroeschke opened this issue Mar 7, 2025 · 2 comments · May be fixed by #61118
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@ZanirP
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Categorical Categorical Data Type Deprecate Functionality to remove in pandas

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@mroeschke
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Currently one can specify dtype="category" to specify data as CategoricalDtype, and since it does not convey ordered information, we treat it as ordered=None internally in order to no-op data that is already categorical. Therefore internally, there are scenarios where we need to be mindful if we have ordered=None vs ordered=True/False

To simplify this gymnastics, it would be great if dtype="category" always meant CategoricalDtype(ordered=False). I think we would only need to issue a deprecation warning when specifying dtype="category" when the data is categorical and ordered=True
@mroeschke mroeschke added Categorical Categorical Data Type Deprecate Functionality to remove in pandas labels Mar 7, 2025
@ZanirP
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ZanirP commented Mar 13, 2025

Hi! I would love to take this!

Just to clarify, the goal is to make dtype="category" always mean CategoricalDtype(ordered=False), with a deprecation warning when applied to CategoricalDtype(ordered=True).

So for example:

cat_ordered = pd.Categorical(["low", "medium", "high"], ordered=True)
categorical_data = cat_ordered.astype("category")

Current behavior is: CategoricalDtype(categories=['high', 'low', 'medium'], ordered=True, categories_dtype=object)
Expected behavior is: CategoricalDtype(categories=['high', 'low', 'medium'], ordered=False, categories_dtype=object) with a deprecation warning being raised (to inform users that ordering is being removed)?

Let me know if this sounds good!

@ZanirP
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ZanirP commented Mar 13, 2025

take

@ZanirP ZanirP linked a pull request Mar 13, 2025 that will close this issue
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Categorical Categorical Data Type Deprecate Functionality to remove in pandas
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BUG/TST/DEPR: Ensure dtype="category" always implies ordered=False & add tests ZanirP/pandas
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@mroeschke @ZanirP