how to change pcolor one grid color on click in matplotlib?

Question

i'm new to python and matplotlib, i want to change grid color on click, but following code can't, how to do it? enter image description here

#!/usr/bin/python
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.colors import LogNorm
import math
     
Z = np.random.rand(25, 25)

Z = []
for x in range(25) :
    sublist = [1]*25
    Z.append(sublist)


fig, ax = plt.subplots()

Z[0][0] = 0
mesh = ax.pcolor(Z,edgecolor= 'k')

def onclick(event):
    print('%s click: button=%d, x=%d, y=%d, xdata=%f, ydata=%f' %
          ('double' if event.dblclick else 'single', event.button,
           event.x, event.y, event.xdata, event.ydata))
    _gx = int(math.floor(event.xdata))
    _gy = int(math.floor(event.ydata))
    print("index x=%d y=%d", _gx,_gy)
    Z[_gy][_gx] = 25
    ax.pcolor(Z)

cid = fig.canvas.mpl_connect('button_press_event', onclick)

plt.title('matplotlib.pyplot.pcolormesh() function Example', fontweight ="bold")
plt.show()

score 0 · Answer 1 · answered Apr 11 '21 at 11:42

There are a few issues:

numpy arrays and lists of lists are quite different concepts, although they both represent a 2D array of values. To address a cell in an numpy array, you need the comma notation: Z[_gy, _gx] = 25
for an interactive it helps to not constantly recreate the same graphical elements; calling ax.pcolor inside the onclick function would continuously create new colormeshes, one on top of the other until the system gets really slow; usually a property of the already created element is updated; mesh.set_array is a way to update the values for the colors
when calling ax.pcolor, setting vmin and vmax tells matplotlib which value correspond to the lowest and which to the highest color; it may also help to explicitly set a colormap (default it would be 'viridis')
fig.canvas.draw() may be needed to show the modified mesh (this depends on the environment in which matplotlib is run)

import matplotlib.pyplot as plt
import numpy as np
import math

def onclick(event):
    print('%s click: button=%d, x=%d, y=%d, xdata=%f, ydata=%f' %
          ('double' if event.dblclick else 'single', event.button,
           event.x, event.y, event.xdata, event.ydata))
    _gx = int(math.floor(event.xdata))
    _gy = int(math.floor(event.ydata))
    print("index x=%d y=%d", _gx, _gy)
    Z[_gy, _gx] = 25
    mesh.set_array(Z.ravel())
    fig.canvas.draw()

Z = np.random.rand(25, 25)

fig, ax = plt.subplots()

mesh = ax.pcolor(Z, edgecolor='k', cmap='plasma', vmin=0, vmax=25)
fig.canvas.mpl_connect('button_press_event', onclick)

plt.title('matplotlib.pyplot.pcolormesh() function Example', fontweight="bold")
plt.show()

Note that Z = np.random.rand(25, 25) creates values between 0 and 1. With vmax=25 this sets some random very dark colors for the background.

how to change pcolor one grid color on click in matplotlib?

1 Answers1