Class Scalar

dask/dataframe/dask_expr/_collection.py:4792–4823

Scalar Expr Collection

class Scalar(FrameBase):
    """Scalar Expr Collection"""

    def __repr__(self):
        return f"<dask_expr.expr.Scalar: expr={self.expr}, dtype={self.dtype}>"

    def __bool__(self):
        raise TypeError(
            f"Trying to convert {self} to a boolean value. Because Dask objects are "
            "lazily evaluated, they cannot be converted to a boolean value or used "
            "in boolean conditions like if statements. Try calling .compute() to "
            "force computation prior to converting to a boolean value or using in "
            "a conditional statement."
        )

    def __dask_postcompute__(self):
        return first, ()

    def to_series(self, index=0) -> Series:
        return new_collection(expr.ScalarToSeries(self, index=index))

    def __array__(self):
        # array interface is required to support pandas instance + Scalar
        # Otherwise, above op results in pd.Series of Scalar (object dtype)
        return np.asarray(self.compute())

    @functools.cached_property
    def dtype(self):
        return pd.Series(self._meta).dtype

    def to_delayed(self, optimize_graph=True):
        return super().to_delayed(optimize_graph=optimize_graph)[0]


def optimize(collection, fuse=True):