Matplotlib imshow/matshow display values on plot

matplotlib, numpy, python, visualization

Solution

Can you do something like:

import numpy as np
import matplotlib.pyplot as plt

fig, ax = plt.subplots()

min_val, max_val = 0, 10
ind_array = np.arange(min_val + 0.5, max_val + 0.5, 1.0)
x, y = np.meshgrid(ind_array, ind_array)

for i, (x_val, y_val) in enumerate(zip(x.flatten(), y.flatten())):
    c = 'x' if i%2 else 'o' 
    ax.text(x_val, y_val, c, va='center', ha='center')
#alternatively, you could do something like
#for x_val, y_val in zip(x.flatten(), y.flatten()):
#    c = 'x' if (x_val + y_val)%2 else 'o'

ax.set_xlim(min_val, max_val)
ax.set_ylim(min_val, max_val)
ax.set_xticks(np.arange(max_val))
ax.set_yticks(np.arange(max_val))
ax.grid()

Edit:

Here is an updated example with an `imshow` background.

import numpy as np
import matplotlib.pyplot as plt

fig, ax = plt.subplots()

min_val, max_val, diff = 0., 10., 1.

#imshow portion
N_points = (max_val - min_val) / diff
imshow_data = np.random.rand(N_points, N_points)
ax.imshow(imshow_data, interpolation='nearest')

#text portion
ind_array = np.arange(min_val, max_val, diff)
x, y = np.meshgrid(ind_array, ind_array)

for x_val, y_val in zip(x.flatten(), y.flatten()):
    c = 'x' if (x_val + y_val)%2 else 'o'
    ax.text(x_val, y_val, c, va='center', ha='center')

#set tick marks for grid
ax.set_xticks(np.arange(min_val-diff/2, max_val-diff/2))
ax.set_yticks(np.arange(min_val-diff/2, max_val-diff/2))
ax.set_xticklabels([])
ax.set_yticklabels([])
ax.set_xlim(min_val-diff/2, max_val-diff/2)
ax.set_ylim(min_val-diff/2, max_val-diff/2)
ax.grid()
plt.show()

Problem

I am trying to create a 10x10 grid using either `imshow` or `matshow` in Matplotlib. The function below takes a numpy array as input, and plots the grid. However, I'd like to have values from the array also displayed inside the cells defined by the grid. So far I could not find a proper way to do it. I can use `plt.text` to place things over the grid, but this requires coordinates of each cell, totally inconvenient. Is there a better way to do what I am trying to accomplish? Thanks! NOTE: The code below does not take the values from the array yet, I was just playing with `plt.text`. ``` import numpy as np import matplotlib.pyplot as plt from matplotlib import colors board = np.zeros((10, 10)) def visBoard(board): cmap = colors.ListedColormap(['white', 'red']) bounds=[0,0.5,1] norm = colors.BoundaryNorm(bounds, cmap.N) plt.figure(figsize=(4,4)) plt.matshow(board, cmap=cmap, norm=norm, interpolation='none', vmin=0, vmax=1) plt.xticks(np.arange(0.5,10.5), []) plt.yticks(np.arange(0.5,10.5), []) plt.text(-0.1, 0.2, 'x') plt.text(0.9, 0.2, 'o') plt.text(1.9, 0.2, 'x') plt.grid() visBoard(board) ``` Output:

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