Store mouse click event coordinates with matplotlib

Question

I am trying to implement a simple mouse click event in matplotlib. I wish to plot a figure then use the mouse to select the lower and upper limits for integration. So far I am able to print the coordinates to screen but not store them for later use in the program. I would also like to exit the connection to the figure after the second mouse click.

Below is the code which currently plots and then prints the coordinates.

My Question(s):

How can I store coordinates from the figure to list? i.e. click = [xpos, ypos]

Is it possible to get two sets of x coordinates in order to do a simple integration over that section of line?

import numpy as np import matplotlib.pyplot as plt  x = np.arange(-10,10) y = x**2  fig = plt.figure() ax = fig.add_subplot(111) ax.plot(x,y)  def onclick(event):     global ix, iy     ix, iy = event.xdata, event.ydata     print 'x = %d, y = %d'%(         ix, iy)      global coords     coords = [ix, iy]      return coords   for i in xrange(0,1):      cid = fig.canvas.mpl_connect('button_press_event', onclick)   plt.show() 

Answer 1

mpl_connect needs to be called just once to connect the event to event handler. It will start listening to click event until you disconnect. And you can use

fig.canvas.mpl_disconnect(cid) 

to disconnect the event hook.

What you want to do is something like:

import numpy as np import matplotlib.pyplot as plt  x = np.arange(-10,10) y = x**2  fig = plt.figure() ax = fig.add_subplot(111) ax.plot(x,y)  coords = []  def onclick(event):     global ix, iy     ix, iy = event.xdata, event.ydata     print 'x = %d, y = %d'%(         ix, iy)      global coords     coords.append((ix, iy))      if len(coords) == 2:         fig.canvas.mpl_disconnect(cid)      return coords cid = fig.canvas.mpl_connect('button_press_event', onclick) 

Answer 2

Thanks to otterb for providing the answer! I've added in a little function taken from here... Find nearest value in numpy array

In all this code will plot, wait for selection of x points and then return the indices of the x array needed for any integration, summations etc.

Ta,

import numpy as np import matplotlib.pyplot as plt from scipy.integrate import trapz  def find_nearest(array,value):     idx = (np.abs(array-value)).argmin()     return array[idx]  # Simple mouse click function to store coordinates def onclick(event):     global ix, iy     ix, iy = event.xdata, event.ydata      # print 'x = %d, y = %d'%(     #     ix, iy)      # assign global variable to access outside of function     global coords     coords.append((ix, iy))      # Disconnect after 2 clicks     if len(coords) == 2:         fig.canvas.mpl_disconnect(cid)         plt.close(1)     return   x = np.arange(-10,10) y = x**2  fig = plt.figure(1) ax = fig.add_subplot(111) ax.plot(x,y)  coords = []  # Call click func cid = fig.canvas.mpl_connect('button_press_event', onclick)  plt.show(1)   # limits for integration ch1 = np.where(x == (find_nearest(x, coords[0][0]))) ch2 = np.where(x == (find_nearest(x, coords[1][0])))  # Calculate integral y_int = trapz(y[ch1[0][0]:ch2[0][0]], x = x[ch1[0][0]:ch2[0][0]])  print '' print 'Integral between '+str(coords[0][0])+ ' & ' +str(coords[1][0]) print y_int