CODEWITHSUNDEEP
pythonmatplotlibconfusion-matrix
Pinkie
Pinkie

Reputation: 163

Confusion Matrix with number of classified/misclassified instances on it (Python/Matplotlib)

I am plotting a confusion matrix with matplotlib with the following code:

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')
cb = fig.colorbar(res)
savefig("confmat.png", format="png")

But I want to the confusion matrix to show the numbers on it like this graphic (the right one). How can I plot the conf_arr on the graphic?

confusion matrix

Upvotes: 10

Views: 7684

Answers (2)

tom10
tom10

Reputation: 69242

You can use text to put arbitrary text in your plot. For example, inserting the following lines into your code will write the numbers (note the first and last lines are from your code to show you where to insert my lines):

res = ax.imshow(array(norm_conf), cmap=cm.jet, interpolation='nearest')
for i, cas in enumerate(conf_arr):
    for j, c in enumerate(cas):
        if c>0:
            plt.text(j-.2, i+.2, c, fontsize=14)
cb = fig.colorbar(res)

matrix with numbers

Upvotes: 10

Justin Peel
Justin Peel

Reputation: 47082

The only way I could really see of doing it was to use annotations. Try these lines:

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))

before saving the figure. It adds the numbers, but I'll let you figure out how to get the sizes of the numbers how you want them.

Upvotes: 1

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