pola-rs/polars · error · ValueError

Enum categories must be unique; found duplicate {duplicate!r

Error message

Enum categories must be unique; found duplicate {duplicate!r}

What it means

Error "Enum categories must be unique; found duplicate {duplicate!r}" thrown in pola-rs/polars.

Source

Thrown at py-polars/src/polars/datatypes/classes.py:1070

        elif not isinstance(categories, pl.Series):
            categories = pl.Series(values=categories)

        if categories.is_empty():
            self.categories = pl.Series(name="category", dtype=String)
            return

        if categories.has_nulls():
            msg = "Enum categories must not contain null values"
            raise TypeError(msg)

        if (dtype := categories.dtype) != String:
            msg = f"Enum categories must be strings; found data of type {dtype}"
            raise TypeError(msg)

        if categories.n_unique() != categories.len():
            duplicate = categories.filter(categories.is_duplicated())[0]
            msg = f"Enum categories must be unique; found duplicate {duplicate!r}"
            raise ValueError(msg)

        self.categories = categories.rechunk().alias("category")

    def __eq__(self, other: PolarsDataType) -> bool:  # type: ignore[override]
        # allow comparing object instances to class
        if type(other) is DataTypeClass and issubclass(other, Enum):
            return True
        elif isinstance(other, Enum):
            return self.categories.equals(other.categories)
        else:
            return False

    def __hash__(self) -> int:
        return hash((self.__class__, tuple(self.categories)))

    def __repr__(self) -> str:
        class_name = self.__class__.__name__
        return f"{class_name}(categories={self.categories.to_list()!r})"

View on GitHub (pinned to df599052da)

When it happens

Trigger: Thrown at py-polars/src/polars/datatypes/classes.py:1070 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of pola-rs/polars@df599052da (2026-08-16). Data as JSON: /api/errors/75fcb7462253ff5b. Report an issue: GitHub.