鼠标悬停事件发生时如何更改饼图切片的颜色

Question

I have created a pie chart in matplotlib . I want to achieve this result in python ie whenever the mouse is hovered on any slice its color is changed .I have searched a lot and came up with the use of bind method but that was not effective though and therefore was not able to come up with the positive result. I will have no problem if this can be done through any other library(say tkinter , plotly ,etc but I need to come up with the solution with matplotlib so I would appreciate that more).Please have a look through my question and any suggestion is warmly welcomed... Here is my code:

import matplotlib.pyplot as plt

labels = 'A', 'B', 'C', 'D'
sizes = [10, 35, 50, 5]
explode = (0, 0, 0.1, 0)  # only "explode" the 3rd slice (i.e. 'C')

fig1, ax1 = plt.subplots()
ax1.pie(sizes, explode=explode, labels=labels, autopct='%1.1f%%',
    shadow=True, startangle=90)
ax1.axis('equal')  # Equal aspect ratio ensures that pie is drawn as a circle.

plt.show()

Regards...

Answer 1

You would need a matplotlib event handler for a motion_notify_event . This can be connected to a function which checks if the mouse is inside one of the pie chart's wedges. This is done via contains_point . In that case colorize the wedge differently, else set its color to its original color.

import matplotlib.pyplot as plt

labels = 'A', 'B', 'C', 'D'
sizes = [10, 35, 50, 5]
explode = (0, 0, 0.1, 0)  # only "explode" the 3rd slice (i.e. 'C')

fig1, ax1 = plt.subplots()
wedges, _, __ = ax1.pie(sizes, explode=explode, labels=labels, autopct='%1.1f%%',
    shadow=True, startangle=90)
ax1.axis('equal')  # Equal aspect ratio ensures that pie is drawn as a circle.

ocols= [w.get_facecolor() for w in wedges]
ncols= ["gold", "indigo", "purple", "salmon"]

def update(event):
    if event.inaxes == ax1:
        for i, w in enumerate(wedges):
            if w.contains_point([event.x, event.y]):
                w.set_facecolor(ncols[i])
            else:
                w.set_facecolor(ocols[i])
        fig1.canvas.draw_idle()


fig1.canvas.mpl_connect("motion_notify_event", update)

plt.show()

Answer 2

First off, what you are looking for is the documentation on Event handling in matplotlib . In particular, the motion_notify_event will be fired every time the mouse moves. However, I can't think of an easy way to identify which wedge the mouse is over right now.

If clicking is acceptable, then the problem is much easier:

labels = 'A', 'B', 'C', 'D'
sizes = [10, 35, 50, 5]
explode = (0, 0, 0.1, 0)  # only "explode" the 3rd slice (i.e. 'C')
click_color = [0.2, 0.2, 0.2]

fig1, ax1 = plt.subplots()
patches, texts, autotexts = ax1.pie(sizes, explode=explode, labels=labels, autopct='%1.1f%%',
    shadow=True, startangle=90)

# store original color inside patch object
# THIS IS VERY HACKY.
# We use the Artist's 'gid' which seems to be unused as far as I can tell
# to be able to recall the original color
for p in patches:
    p.set_gid(p.get_facecolor())
    # enable picking
    p.set_picker(True)

ax1.axis('equal')  # Equal aspect ratio ensures that pie is drawn as a circle.


def on_pick(event):
    #restore all facescolor to erase previous changes
    for p in patches:
        p.set_facecolor(p.get_gid())
    a = event.artist
    # print('on pick:', a, a.get_gid())
    a.set_facecolor(click_color)
    plt.draw()

fig1.canvas.mpl_connect('pick_event', on_pick)
plt.show()