Plot a 2D array with axes labelled with the array values of a 1D array

Question

I have a 1D array arr1d = ['A', 'B', 'C', 'D'] and I have a 2D array

arr2d =[[1, 2, 5, 3], [2, 1, 2, 5], [5, 3, 4, 4], [5, 5, 3, 4]] (say) I wish to plot the array using matplotlib (or any other library) in such a way that the output is in the following manner. I want the x and y axis to get labelled as per the 1D array as shown in the picture. How to achieve that?

Answer 1

You could try something like this:

from matplotlib import pyplot as plt
from matplotlib import colors
import numpy as np

arr1d = ['A', 'B', 'C', 'D']
data = np.array([[1, 2, 5, 3], [2, 1, 2, 5], [5, 3, 4, 4], [5, 5, 3, 4]])
cmap = colors.ListedColormap(['blue','red', 'green', 'yellow', 'cyan'])
fig, ax = plt.subplots()
ax.imshow(data, cmap=cmap)

for (i, j), z in np.ndenumerate(data):
    ax.text(j, i, '{}'.format(z), ha='center', va='center', size=12)
    
plt.xticks(np.arange(len(arr1d)), arr1d)
plt.yticks(np.arange(len(arr1d)), arr1d)
plt.show()

Using ListedColormap, you can decide which number is mapped to which color.

Or with grid lines:

from matplotlib import pyplot as plt
from matplotlib import colors
import numpy as np
from matplotlib.ticker import (AutoMinorLocator, MultipleLocator)

arr1d = ['A', 'B', 'C', 'D']
data = np.array([[1, 2, 5, 3], [2, 1, 2, 5], [5, 3, 4, 4], [5, 5, 3, 4]])
cmap = colors.ListedColormap(['blue','red', 'green', 'yellow', 'cyan'])

_, ax = plt.subplots()
for (i, j), z in np.ndenumerate(data):
  ax.annotate('{}'.format(z), xy = (j + 0.4, i + 0.6), fontsize=15)

ax.imshow(data, cmap=cmap, extent=(0, data.shape[0], data.shape[1], 0))
ax.grid(color='black', linewidth=3)

plt.xticks(np.arange(len(arr1d)), arr1d)
plt.yticks(np.arange(len(arr1d)), arr1d)
plt.show()

Answer 2

You could achieve a result close to what you need with matshow in matplotlib.

import matplotlib.pyplot as plt
arr1d = ['A', 'B', 'C', 'D']
arr2d =[[1, 2, 5, 3], [2, 1, 2, 5], [5, 3, 4, 4], [5, 5, 3, 4]]
plt.matshow(arr2d)
plt.xticks([0,1,2,3], arr1d)
plt.yticks([0,1,2,3], arr1d)
plt.show()