用自定义颜色在Python中绘制矩阵

Question

I'm trying to plot a matrix using pytlot in python.

import matplotlib.pyplot as plt
m = [
    [1, 0, 2, 0, 0],
    [1, 1, 1, 2, 0],
    [0, 4, 1, 0, 0],
    [0, 4, 4, 1, 2],
    [1, 3, 0, 0, 1],
]

plt.imshow(m)

plt.show()

This look like what I need, but the problem is that I need to be able to select the color for a position.

For example:

the position 1x2 has to be red.

anyway to archive this with Python and Pyplot?

Answer 1

You can map a certain range to a certain colormap using the vmin and vmax arguments, and then assign those colors to particular values in your graph. Here is a simple example, using the brg cmap .

I used 1-10 as a scale, so 1 will be Blue, 5 will be Red, and 10 will be Green, etc.

import matplotlib.pyplot as plt

m = [
    [1, 0, 2, 0, 0],
    [1, 1, 1, 2, 0],
    [0, 4, 1, 0, 0],
    [0, 4, 4, 1, 2],
    [1, 3, 0, 0, 1]
]

dct = {1: 5., 0: 1., 2: 1., 3: 1., 4: 1.}
n = [[dct[i] for i in j] for j in m]
print(n)

plt.imshow(n, cmap='brg', vmin=1, vmax=10)
plt.show()

Output (All 1's in your matrix are now red, all other values set to blue):

Answer 2

I guess that matplotlib.colors.ListedColormap is what you need here:

import matplotlib
import matplotlib.pyplot as plt

colors = 'lime red blue magenta yellow'.split()
cmap = matplotlib.colors.ListedColormap(colors, name='colors', N=None)

m = [
    [1, 0, 2, 0, 0],
    [1, 1, 1, 2, 0],
    [0, 4, 1, 0, 0],
    [0, 4, 4, 1, 2],
    [1, 3, 0, 0, 1],
]

plt.imshow(m, cmap=cmap)
plt.show()

You may also use (R,G,B) tuples (instead of predefined color strings) in your list if you need more control