Lasso Demo

Show how to use a lasso to select a set of points and get the indices of the selected points. A callback is used to change the color of the selected points

This is currently a proof-of-concept implementation (though it is usable as is). There will be some refinement of the API.

from matplotlib import colors as mcolors, path
from matplotlib.collections import RegularPolyCollection
import matplotlib.pyplot as plt
from matplotlib.widgets import Lasso
import numpy as np


class Datum:
    colorin = mcolors.to_rgba("red")
    colorout = mcolors.to_rgba("blue")

    def __init__(self, x, y, include=False):
        self.x = x
        self.y = y
        if include:
            self.color = self.colorin
        else:
            self.color = self.colorout


class LassoManager:
    def __init__(self, ax, data):
        self.axes = ax
        self.canvas = ax.figure.canvas
        self.data = data

        self.Nxy = len(data)

        facecolors = [d.color for d in data]
        self.xys = [(d.x, d.y) for d in data]
        self.collection = RegularPolyCollection(
            6, sizes=(100,),
            facecolors=facecolors,
            offsets=self.xys,
            transOffset=ax.transData)

        ax.add_collection(self.collection)

        self.cid = self.canvas.mpl_connect('button_press_event', self.on_press)

    def callback(self, verts):
        facecolors = self.collection.get_facecolors()
        p = path.Path(verts)
        ind = p.contains_points(self.xys)
        for i in range(len(self.xys)):
            if ind[i]:
                facecolors[i] = Datum.colorin
            else:
                facecolors[i] = Datum.colorout

        self.canvas.draw_idle()
        self.canvas.widgetlock.release(self.lasso)
        del self.lasso

    def on_press(self, event):
        if self.canvas.widgetlock.locked():
            return
        if event.inaxes is None:
            return
        self.lasso = Lasso(event.inaxes,
                           (event.xdata, event.ydata),
                           self.callback)
        # acquire a lock on the widget drawing
        self.canvas.widgetlock(self.lasso)


if __name__ == '__main__':

    np.random.seed(19680801)

    data = [Datum(*xy) for xy in np.random.rand(100, 2)]
    ax = plt.axes(xlim=(0, 1), ylim=(0, 1), autoscale_on=False)
    ax.set_title('Lasso points using left mouse button')

    lman = LassoManager(ax, data)

    plt.show()