radar_chart.py

import numpy as np

import matplotlib.pyplot as plt
from matplotlib.projections.polar import PolarAxes
from matplotlib.projections import register_projection


def radar(num_vars, frame='circle'):
    theta = np.linspace(0, 2 * np.pi, num_vars, endpoint=False)

    # rotate theta such that the first axis is at the top
    theta += np.pi / 2

    def draw_poly_patch(self):
        verts = unit_poly_verts(theta)
        return plt.Polygon(verts, closed=True)

    def draw_circle_patch(self):
        # unit circle centered on (0.5, 0.5)
        return plt.Circle((0.5, 0.5), 0.5)

    patch_dict = {'polygon': draw_poly_patch, 'circle': draw_circle_patch}
    if frame not in patch_dict:
        raise ValueError('unknown value for `frame`: %s' % frame)

    class RadarAxes(PolarAxes):
        name = 'radar'
        # use 1 line segment to connect specified points
        RESOLUTION = 1
        # define draw_frame method
        draw_patch = patch_dict[frame]

        def fill(self, *args, **kwargs):
            """Override fill so that line is closed by default"""
            closed = kwargs.pop('closed', True)
            return super(RadarAxes, self).fill(closed=closed, *args, **kwargs)

        def plot(self, *args, **kwargs):
            """Override plot so that line is closed by default"""
            lines = super(RadarAxes, self).plot(*args, **kwargs)
            for line in lines:
                self._close_line(line)

        def _close_line(self, line):
            x, y = line.get_data()
            # FIXME: markers at x[0], y[0] get doubled-up
            if x[0] != x[-1]:
                x = np.concatenate((x, [x[0]]))
                y = np.concatenate((y, [y[0]]))
                line.set_data(x, y)

        def set_varlabels(self, labels):
            self.set_thetagrids(np.degrees(theta), labels)

        def _gen_axes_patch(self):
            return self.draw_patch()

        def _gen_axes_spines(self):
            return PolarAxes._gen_axes_spines(self)

    register_projection(RadarAxes)
    return theta


def unit_poly_verts(theta):
    """Return vertices of polygon for subplot axes.

    This polygon is circumscribed by a unit circle centered at (0.5, 0.5)
    """
    x0, y0, r = [0.5] * 3
    verts = [(r * np.cos(t) + x0, r * np.sin(t) + y0) for t in theta]
    return verts


def _test():
    labels = 'val1 val2 val3 val4 val5 val6 val7'.split()
    values = [1, 7, 2, 0, 3, 10, 6]
    theta = radar(len(labels))
    fig, ax = plt.subplots(subplot_kw={'projection': 'radar'})
    ax.plot(theta, values, color='k')
    ax.fill(theta, values, color="r")
    ax.set_varlabels(labels)
    ax.set_ylim(0, max(values))

    plt.show()


if __name__ == '__main__':
    _test()