Alternate Colors In Stacked Matplotlib Bar

I'm generating a stacked bar chart in matplotlib (using Python 2.7 on Windows 7). Since I want to use it to pairwise compare data from 2 data-sets, I would like to use different co

Solution 1:

You can do this more elegantly with slicing. A possibly better solution would be to de-interlace your data.

IDs = ["1","A","2","B","3","C","4","D","5","E"]

N = len(IDs)
fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)

set_count = 2
set_label = np.vstack([j*ones(len(IDs)//set_count) for j in range(set_count)]).T.ravel()

property1 = numpy.array([1,3,4,2,3,5,6,7,3,2])
property2 = numpy.array(range(10))
property3 = numpy.array(range(10,0,-1))

props = [property1,property2,property3]

ind = numpy.arange(N/set_count)
width = 0.9
b_width = 0.9/set_count

color_sets = [['red','green','blue'],['black','magenta','yellow']]

for j in range(set_count):
    tmp_accum = np.zeros(len(props[0]))
    for k in range(len(props)):
        ax1.bar(ind +j*b_width, props[k][set_label==j], width=b_width, color=color_sets[j][k], bottom=tmp_accum[set_label==j])
        tmp_accum += props[k]


lab_ind = []
for j in range(set_count):

    lab_ind.append(ind + (j+.5)*b_width)

plt.xticks(np.vstack(lab_ind).T.ravel(), IDs )

It needs some sanity checks, but it works and should scale to more than 2 classes and more than 3 properties easily (you just need to make sure that all of your lengths sync up, using itertools.cycle for the colors might help).

Solution 2:

Found a way that works, although it seems pretty unelegant:

import numpy
import matplotlib.pyplot as plt

fig = plt.figure()
ax1 = fig.add_subplot(1,1,1)

IDs = ["1","A","2","B","3","C","4","D","5","E"]

N = len(IDs)

property1_1 = numpy.array([1,0,4,0,3,0,6,0,3,0])
property1_2 = numpy.array([0,3,0,2,0,5,0,7,0,2])
property2_1 = numpy.array([1,0,2,0,3,0,4,0,5,0])
property2_2 = numpy.array([0,6,0,7,0,8,0,9,0,10])
property3_1 = numpy.array([10,0,9,0,8,0,7,0,6,0])
property3_2 = numpy.array([0,5,0,4,0,3,0,2,0,1])

ind = numpy.arange(N)
width = 0.8

p1 = ax1.bar(ind, property1_1, width, color='red')
p2 = ax1.bar(ind, property2_1, width, color='blue', bottom=property1_1)
p3 = ax1.bar(ind, property3_1, width, color='green', bottom=property1_1 + property2_1)

p4 = ax1.bar(ind-0.2, property1_2, width, color='#FF6666')
p5 = ax1.bar(ind-0.2, property2_2, width, color='#6699FF', bottom=property1_2)
p6 = ax1.bar(ind-0.2, property3_2, width, color='#33CC33', bottom=property1_2+property2_2)
plt.xticks(ind+width/2., IDs )

plt.show()
plt.close()

This is how I did it for the sake of others having this issue. I don't think this is optimal and would appreciate additional answers.