Source code for plotnine.stats.stat_hull

import numpy as np
import pandas as pd

from ..doctools import document
from .stat import stat


@document
class stat_hull(stat):
    """
    2 Dimensional Convex Hull

    {usage}

    Parameters
    ----------
    {common_parameters}
    qhull_options: str, optional
        Additional options to pass to Qhull.
        See `Qhull <http://www.qhull.org/>`__ documentation
        for details.

    Raises
    ------
    QhullError
        Raised when Qhull encounters an error condition,
        such as geometrical degeneracy when options to resolve are
        not enabled.
    """

    _aesthetics_doc = """
    {aesthetics_table}

    .. rubric:: Options for computed aesthetics

    ::

        'area'  # Area of the convex hull

    """
    REQUIRED_AES = {"x", "y"}
    DEFAULT_PARAMS = {
        "geom": "path",
        "position": "identity",
        "na_rm": False,
        "qhull_options": None,
    }
    CREATES = {"area"}

    @classmethod
    def compute_group(cls, data, scales, **params):
        from scipy.spatial import ConvexHull

        hull = ConvexHull(
            data[["x", "y"]], qhull_options=params["qhull_options"]
        )
        idx = np.hstack([hull.vertices, hull.vertices[0]])

        new_data = pd.DataFrame(
            {
                "x": data["x"].iloc[idx].values,
                "y": data["y"].iloc[idx].values,
                "area": hull.area,
            }
        )
        return new_data