Method join

dask/dataframe/dask_expr/_collection.py:2981–3026

(
        self,
        other,
        on=None,
        how="left",
        lsuffix="",
        rsuffix="",
        shuffle_method=None,
        npartitions=None,
    )

    @derived_from(pd.DataFrame)
    def join(
        self,
        other,
        on=None,
        how="left",
        lsuffix="",
        rsuffix="",
        shuffle_method=None,
        npartitions=None,
    ):
        if not isinstance(other, list) and not is_dask_collection(other):
            other = from_pandas(other, npartitions=1)
        if (
            not isinstance(other, list)
            and not is_dataframe_like(other._meta)
            and hasattr(other._meta, "name")
        ):
            other = new_collection(expr.ToFrame(other))

        if not isinstance(other, FrameBase):
            if not isinstance(other, list) or not all(
                isinstance(o, FrameBase) for o in other
            ):
                raise ValueError("other must be DataFrame or list of DataFrames")
            if how not in ("outer", "left"):
                raise ValueError("merge_multi only supports left or outer joins")

            other = [
                from_pandas(o, npartitions=1) if not is_dask_collection(o) else o
                for o in other
            ]

            return new_collection(
                JoinRecursive([self.expr] + [o.expr for o in other], how=how)
            )

        return self.merge(
            right=other,
            left_index=on is None,
            right_index=True,
            left_on=on,
            how=how,
            suffixes=(lsuffix, rsuffix),
            shuffle_method=shuffle_method,
            npartitions=npartitions,
        )

    @derived_from(pd.DataFrame)
    def groupby(