More efficient matplotlib stacked bar chart - how to calculate bottom values

Question

I need some help making a set of stacked bar charts in python with matlibplot. My basic code is below but my problems is how to generate the value for bottom for any element beyond the 2nd one efficiently. I can get the example graph to stack correctly (always a,b,c,d from bottom to top)

import numpy as np
import matplotlib.pyplot as plt

ind = np.arange(3)

a = [3,6,9]
b = [2,7,1]
c = [0,3,1]
d = [4,0,3]

p1 = plt.bar(ind, a, 1, color='#ff3333')
p2 = plt.bar(ind, b, 1, color='#33ff33', bottom=a)
p3 = plt.bar(ind, c, 1, color='#3333ff', bottom=[a[j] +b[j] for j in range(len(a))])
p4 = plt.bar(ind, d, 1, color='#33ffff', bottom=[a[j] +b[j] +c[j] for j in range(len(a))])

plt.show()

My final code could have very large number of bars and the ever expanding function bottom = [...] cannot be the best solution. It would be great if you could also explain how I need to derive the value. Is there a numpy function.

Thank you very much!!! PS I have searched for an answer but I did not understand what I could find.

Answer 1

I have just recently faced the same problem. Afterwards I decided to wrap it all up in a nice class. For anyone interested you get an implementation of a stacked bar graph class here:

https://github.com/minillinim/stackedBarGraph

It allows scaled stacked graphs as well as setting bar widths and set heights (with scaled inners).

Given a data set like this:

    d = np.array([[101.,0.,0.,0.,0.,0.,0.],
                  [92.,3.,0.,4.,5.,6.,0.],
                  [56.,7.,8.,9.,23.,4.,5.],
                  [81.,2.,4.,5.,32.,33.,4.],
                  [0.,45.,2.,3.,45.,67.,8.],
                  [99.,5.,0.,0.,0.,43.,56.]])

    d_heights = [1.,2.,3.,4.,5.,6.]
    d_widths = [.5,1.,3.,2.,1.,2.]
    d_labels = ["fred","julie","sam","peter","rob","baz"]
    d_colors = ['#2166ac',
                '#fee090',
                '#fdbb84',
                '#fc8d59',
                '#e34a33',
                '#b30000',
                '#777777']

It can make images like this:

GPLv3 with love.