Assign specific colours to data in Matplotlib pie chart

Question

I'm trying to create pie charts with matplotlib in which the colour of each category is fixed.

I've got a function which creates a pie chart from sets of value and category data. Here's one example:

Category     Value
TI           65
Con          43
FR           40
TraI         40
Bug          38
Data         22
Int          15
KB           12
Other        8
Dep          7
PW           6
Uns          5
Perf         4
Dep          3

The problem is that the data differs from one instance to another, and that in turn changes the order of the categories. Thus, each category gets labelled a different colour each time I generate a chart. I could sort the data alphabetically every time, but that causes two problems: some categories are missing from some datasets, and I'd prefer it sorted by size anyway so that the smallest wedges are oriented horizontally.

How can I set matplotlib to assign colours depending on, say, the index of a pandas.Series?

Here's the code that I'm using to generate a pie chart:

import matplotlib.pyplot as plt

slices = [62, 39, 39, 38, 37, 21, 15,  9,  6,  7,  6,  5,  4, 3]

cmap = plt.cm.prism
colors = cmap(np.linspace(0., 1., len(slices)))

labels = [u'TI', u'Con', u'FR', u'TraI', u'Bug', u'Data', u'Int', u'KB', u'Other', u'Dep', u'PW', u'Uns', u'Perf', u'Dep']

fig = plt.figure(figsize=[10, 10])
ax = fig.add_subplot(111)

pie_wedge_collection = ax.pie(slices, colors=colors, labels=labels, labeldistance=1.05, autopct=make_autopct(slices))

for pie_wedge in pie_wedge_collection[0]:
    pie_wedge.set_edgecolor('white')

titlestring = 'Issues'

ax.set_title(titlestring)

EDIT: I forgot to explain the autopct function, it's for adding value and percentage labels:

def make_autopct(values):
    def my_autopct(pct):
        total = sum(values)
        val = int(round(pct*total/100.0))
        return '{p:.2f}%  ({v:d})'.format(p=pct,v=val)
    return my_autopct

Answer 1

Here's an idea you could try. Make a dictionary from your labels and colors, so each color is mapped to a label. Then, after making the pie chart, go in an assign the facecolor of the wedge using this dictionary.

Here's an untested bit of code which might do what you are looking for:

import numpy as np
import matplotlib.pyplot as plt

def mypie(slices,labels,colors):

    colordict={}
    for l,c in zip(labels,colors):
        print l,c
        colordict[l]=c

    fig = plt.figure(figsize=[10, 10])
    ax = fig.add_subplot(111)

    pie_wedge_collection = ax.pie(slices, labels=labels, labeldistance=1.05)#, autopct=make_autopct(slices))

    for pie_wedge in pie_wedge_collection[0]:
        pie_wedge.set_edgecolor('white')
        pie_wedge.set_facecolor(colordict[pie_wedge.get_label()])

    titlestring = 'Issues'

    ax.set_title(titlestring)

    return fig,ax,pie_wedge_collection

slices = [37, 39, 39, 38, 62, 21, 15,  9,  6,  7,  6,  5,  4, 3]
cmap = plt.cm.prism
colors = cmap(np.linspace(0., 1., len(slices)))
labels = [u'TI', u'Con', u'FR', u'TraI', u'Bug', u'Data', u'Int', u'KB', u'Other', u'Dep', u'PW', u'Uns', u'Perf', u'Dep']

fig,ax,pie_wedge_collection = mypie(slices,labels,colors)

plt.show()