Plotting a pie-chart in matplotlib at a specific angle with the fracs on the wedges

问题

I am plotting a piechart with matplotlib using the following code:

ax = axes([0.1, 0.1, 0.6, 0.6])
labels = 'Twice Daily', 'Daily', '3-4 times per week', 'Once per week','Occasionally'
fracs = [20,50,10,10,10]

explode=(0, 0, 0, 0,0.1)
patches, texts, autotexts = ax.pie(fracs, labels=labels, explode = explode,         
                             autopct='%1.1f%%', shadow =True)
proptease = fm.FontProperties()
proptease.set_size('xx-small')
setp(autotexts, fontproperties=proptease)
setp(texts, fontproperties=proptease)
rcParams['legend.fontsize'] = 7.0
savefig("pie1")

This produces the following piechart.

However, I want to start the pie-chart with the first wedge on top, the only solution I could find for this was using this code

However on using this as below,

from pylab import *
from matplotlib import font_manager as fm
from matplotlib.transforms import Affine2D
from matplotlib.patches import Circle, Wedge, Polygon
import numpy as np

fig = plt.figure()
ax = fig.add_subplot(111)

labels = 'Twice Daily', 'Daily', '3-4 times per week', 'Once per week','Occasionally'
fracs = [20,50,10,10,10]

 wedges, plt_labels = ax.pie(fracs, labels=labels)
 ax.axis('equal')

 starting_angle = 90
 rotation = Affine2D().rotate(np.radians(starting_angle))

for wedge, label in zip(wedges, plt_labels):
  label.set_position(rotation.transform(label.get_position()))
  if label._x > 0:
    label.set_horizontalalignment('left')
  else:
    label.set_horizontalalignment('right')

  wedge._path = wedge._path.transformed(rotation)

plt.savefig("pie2")

This produces the following pie chart

However, this does not print the fracs on the wedges as in the earlier pie chart. I have tried a few different things, but I am not able to preserve the fracs. How can I start the first wedge at noon and display the fracs on the wedges as well??

回答1:

Ordinarily I wouldn't recommend changing the source of a tool, but it's hacky to fix this outside and easy inside. So here's what I'd do if you needed this to work Right Now(tm), and sometimes you do..

In the file matplotlib/axes.py, change the declaration of the pie function to

def pie(self, x, explode=None, labels=None, colors=None,
        autopct=None, pctdistance=0.6, shadow=False,
        labeldistance=1.1, start_angle=None):

i.e. simply add start_angle=None to the end of the arguments.

Then add the five lines bracketed by "# addition".

    for frac, label, expl in cbook.safezip(x,labels, explode):
        x, y = center
        theta2 = theta1 + frac
        thetam = 2*math.pi*0.5*(theta1+theta2)

        # addition begins here
        if start_angle is not None and i == 0:
            dtheta = (thetam - start_angle)/(2*math.pi)
            theta1 -= dtheta
            theta2 -= dtheta
            thetam = start_angle
        # addition ends here

        x += expl*math.cos(thetam)
        y += expl*math.sin(thetam)

Then if start_angle is None, nothing happens, but if start_angle has a value, then that's the location that the first slice (in this case the 20%) is centred on. For example,

patches, texts, autotexts = ax.pie(fracs, labels=labels, explode = explode,         
                             autopct='%1.1f%%', shadow =True, start_angle=0.75*pi)

produces

Note that in general you should avoid doing this, patching the source I mean, but there are times in the past when I've been on deadline and simply wanted something Now(tm), so there you go..

来源：https://stackoverflow.com/questions/9220933/plotting-a-pie-chart-in-matplotlib-at-a-specific-angle-with-the-fracs-on-the-wed

标签

python

matplotlib

pie-chart

wedge