如何使用matplotlib绘制没有颜色网格的混淆矩阵？

Question

我在如何使用字符串轴而不是python中的整数绘制混淆矩阵时发现了类似的问题。 但答案并不完全是我想要的。 因为它不包含网格（例如，数字不在小方块中）并且有背景颜色来显示不是我想要的数字。

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')

Answer 1

通过对相当优秀的代码提案进行一些更改（我赞成它，考虑也这样做），您可以获得您描述的数字。

您将通过调用ax对象的hlines和vlines方法来获取网格，这将分别添加水平和垂直线。 当你然后删除对imshow的调用时，颜色消失了。 像这样：

import numpy as np
import matplotlib.pyplot as plt

conf_arr = np.array([[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]])
height, width = conf_arr.shape

fig = plt.figure('confusion matrix')
ax = fig.add_subplot(111, aspect='equal')
for x in range(width):
    for y in range(height):
        ax.annotate(str(conf_arr[x][y]), xy=(y, x), ha='center', va='center')

offset = .5    
ax.set_xlim(-offset, width - offset)
ax.set_ylim(-offset, height - offset)

ax.hlines(y=np.arange(height+1)- offset, xmin=-offset, xmax=width-offset)
ax.vlines(x=np.arange(width+1) - offset, ymin=-offset, ymax=height-offset)

alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
plt.xticks(range(width), alphabet[:width])
plt.yticks(range(height), alphabet[:height])
plt.savefig('confusion_matrix.png', format='png')

注意当您删除对imshow的调用时，您需要明确设置x和y限制，如上所示，否则您将只看到左下区域（ imshow根据您通过的内容自动更新限制它）。