I have the following plot

import numpy as np
import matplotlib.pyplot as plt

a = np.random.randn(4,4)
fig, ax = plt.subplots()
im = ax.imshow(a)
plt.axis('off')
plt.show()

output:

I am trying to add the following gridlines:

gridlines = np.array([
  [0,2], [2,4],
  [0,4],
  [0,3], [3,4],
  [0,1], [1,3],
])

such that the plot looks like this:

Finally, I want to add text in the center of each red rectangle:

Is there any documentation or tutorial for doing this with matplotlib?

CodePudding user response：

Since you have define gridlines, it is easy to achieve that result by adding Rectangles and text annotations.

Note that in the following I have modified gridlines to be a dictionary, mapping each "row" to grids.

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import Rectangle

gridlines = {
  0: [[0,2], [2,4]],
  1: [[0,4]],
  2: [[0,3], [3,4]],
  3: [[0,1], [1,3]],
}

a = np.random.randn(4,4)
fig, ax = plt.subplots()
im = ax.imshow(a)
plt.axis('off')

xmin, xmax = ax.get_xlim()
ymin, ymax = ax.get_ylim()
dx = (xmax - xmin) / 4
dy = (ymax - ymin) / 4

count = 1
for r, v in gridlines.items():
    for (_xmin, _xmax) in v:
        x = xmin   dx * _xmin
        y = ymax - (r   1) * dy
        w = dx * (_xmax - _xmin)
        ax.add_patch(Rectangle((x, y), w, dy, facecolor='none', edgecolor="r", linewidth=3))
        ax.text(x   w / 2, ymax - (r   1) * dy   dy / 2, "text%s" % count, ha="center", va="center", color="white")
        count  = 1
    
plt.show()