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() ax = fig.add_subplot(111) 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

Answer 1

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 = fig.add_subplot(111) 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')