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# Lasso Selector Demo

    from __future__ import print_function

    from six.moves import input

    import numpy as np

    from matplotlib.widgets import LassoSelector
    from matplotlib.path import Path

    class SelectFromCollection(object):
        """Select indices from a matplotlib collection using `LassoSelector`.

        Selected indices are saved in the `ind` attribute. This tool fades out the
        points that are not part of the selection (i.e., reduces their alpha
        values). If your collection has alpha < 1, this tool will permanently
        alter the alpha values.

        Note that this tool selects collection objects based on their *origins*
        (i.e., `offsets`).

        Parameters
        ----------
        ax : :class:`~matplotlib.axes.Axes`
            Axes to interact with.

        collection : :class:`matplotlib.collections.Collection` subclass
            Collection you want to select from.

        alpha_other : 0 <= float <= 1
            To highlight a selection, this tool sets all selected points to an
            alpha value of 1 and non-selected points to `alpha_other`.
        """

        def __init__(self, ax, collection, alpha_other=0.3):
            self.canvas = ax.figure.canvas
            self.collection = collection
            self.alpha_other = alpha_other

            self.xys = collection.get_offsets()
            self.Npts = len(self.xys)

            # Ensure that we have separate colors for each object
            self.fc = collection.get_facecolors()
            if len(self.fc) == 0:
                raise ValueError('Collection must have a facecolor')
            elif len(self.fc) == 1:
                self.fc = np.tile(self.fc, (self.Npts, 1))

            self.lasso = LassoSelector(ax, onselect=self.onselect)
            self.ind = []

        def onselect(self, verts):
            path = Path(verts)
            self.ind = np.nonzero(path.contains_points(self.xys))[0]
            self.fc[:, -1] = self.alpha_other
            self.fc[self.ind, -1] = 1
            self.collection.set_facecolors(self.fc)
            self.canvas.draw_idle()

        def disconnect(self):
            self.lasso.disconnect_events()
            self.fc[:, -1] = 1
            self.collection.set_facecolors(self.fc)
            self.canvas.draw_idle()

    if __name__ == '__main__':
        import matplotlib.pyplot as plt

        plt.ion()
        # Fixing random state for reproducibility
        np.random.seed(19680801)

        data = np.random.rand(100, 2)

        subplot_kw = dict(xlim=(0, 1), ylim=(0, 1), autoscale_on=False)
        fig, ax = plt.subplots(subplot_kw=subplot_kw)

        pts = ax.scatter(data[:, 0], data[:, 1], s=80)
        selector = SelectFromCollection(ax, pts)

        plt.draw()
        input('Press Enter to accept selected points')
        print("Selected points:")
        print(selector.xys[selector.ind])
        selector.disconnect()

        # Block end of script so you can check that the lasso is disconnected.
        input('Press Enter to quit')

Total running time of the script: ( 0 minutes 0.000 seconds)

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