"""

==========

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.

.. note::

This example exercises the interactive capabilities of Matplotlib, and this

will not appear in the static documentation. Please run this code on your

machine to see the interactivity.

You can copy and paste individual parts, or download the entire example

using the link at the bottom of the page.

"""

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,

offset_transform=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()