# How to plot confusion matrix with string axis rather than integer in python

### Question

I am following a previous thread on how to plot confusion matrix in Matplotlib. The script is as follows:

``````from numpy import *
import matplotlib.pyplot as plt
from pylab import *

conf_arr = [[33,2,0,0,0,0,0,0,0,1,3], [3,31,0,0,0,0,0,0,0,0,0], [0,4,41,0,0,0,0,0,0,0,1], [0,1,0,30,0,6,0,0,0,0,1], [0,0,0,0,38,10,0,0,0,0,0], [0,0,0,3,1,39,0,0,0,0,4], [0,2,2,0,4,1,31,0,0,0,2], [0,1,0,0,0,0,0,36,0,2,0], [0,0,0,0,0,0,1,5,37,5,1], [3,0,0,0,0,0,0,0,0,39,0], [0,0,0,0,0,0,0,0,0,0,38] ]

norm_conf = []
for i in conf_arr:
a = 0
tmp_arr = []
a = sum(i,0)
for j in i:
tmp_arr.append(float(j)/float(a))
norm_conf.append(tmp_arr)

plt.clf()
fig = plt.figure()
res = ax.imshow(array(norm_conf), cmap=cm.jet, interpolation='nearest')

for i,j in ((x,y) for x in xrange(len(conf_arr))
for y in xrange(len(conf_arr[0]))):
ax.annotate(str(conf_arr[i][j]),xy=(i,j))

cb = fig.colorbar(res)
savefig("confusion_matrix.png", format="png")
``````

I would like to change the axis to show string of letters, say (A, B, C,...) rather than integers (0,1,2,3, ..10). How can one do that. Thanks.

musa

1
27
4/28/2011 6:41:49 PM

Here's what I'm guessing you want:

``````import numpy as np
import matplotlib.pyplot as plt

conf_arr = [[33,2,0,0,0,0,0,0,0,1,3],
[3,31,0,0,0,0,0,0,0,0,0],
[0,4,41,0,0,0,0,0,0,0,1],
[0,1,0,30,0,6,0,0,0,0,1],
[0,0,0,0,38,10,0,0,0,0,0],
[0,0,0,3,1,39,0,0,0,0,4],
[0,2,2,0,4,1,31,0,0,0,2],
[0,1,0,0,0,0,0,36,0,2,0],
[0,0,0,0,0,0,1,5,37,5,1],
[3,0,0,0,0,0,0,0,0,39,0],
[0,0,0,0,0,0,0,0,0,0,38]]

norm_conf = []
for i in conf_arr:
a = 0
tmp_arr = []
a = sum(i, 0)
for j in i:
tmp_arr.append(float(j)/float(a))
norm_conf.append(tmp_arr)

fig = plt.figure()
plt.clf()
ax.set_aspect(1)
res = ax.imshow(np.array(norm_conf), cmap=plt.cm.jet,
interpolation='nearest')

width, height = conf_arr.shape

for x in xrange(width):
for y in xrange(height):
ax.annotate(str(conf_arr[x][y]), xy=(y, x),
horizontalalignment='center',
verticalalignment='center')

cb = fig.colorbar(res)
alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
plt.xticks(range(width), alphabet[:width])
plt.yticks(range(height), alphabet[:height])
plt.savefig('confusion_matrix.png', format='png')
``````
61
1/20/2016 10:55:55 PM