plotting scatter plot with 4 colors in python-CodePudding

I want to plot a scatter plot with 4 specified colors of my choice, preferably a good combination with RGB, when provided a weighting array like the following example where I am plotting with 3 colors.

import numpy as np
import matplotlib.pyplot as plt
x = np.array([1,2])
y = np.array([[2,3],[1,4]])

color = [[0.8, 0.1, 0.1],
         [0.1, 0.8, 0.1],
         [0.1, 0.1, 0.8],
         [0.1, 0.8, 0.1]]

plt.scatter(np.repeat(x, y.shape[1]), y.flat, s=100, c=color)

Since by default python makes this an RGB plot the plot looks like this --

Now, If I want to plot with a color array that has 4 elements the plot is not so good to illustrate information in useful way in the RGBA plot.

import numpy as np
import matplotlib.pyplot as plt
x = np.array([1,2])
y = np.array([[2,3],[1,4]])

color = [[0.9, 0.1, 0.1, 0.1],
         [0.1, 0.9, 0.1, 0.1],
         [0.1, 0.1, 0.9, 0.1],
         [0.1, 0.1, 0.1, 0.9]]

plt.scatter(np.repeat(x, y.shape[1]), y.flat, s=100, c=color)

because the plot looks like this --

what is the best way to have specified colors, for example, red, green, blue and golden?

CodePudding user response：

You can just select and use hex values if you need a specific color.

color = ['#ff0000', '#00ff5d', '#0092ff', '#ffe800']

import numpy as np
import matplotlib.pyplot as plt
x = np.array([1,2])
y = np.array([[2,3],[1,4]])

color = ['#ff0000', '#00ff5d', '#0092ff', '#ffe800']

plt.scatter(np.repeat(x, y.shape[1]), y.flat, s=100, c=color)
plt.show()

CodePudding user response：

You can create a RGBA array and then scale it accoardingly (the values inside the array have to be float values in [0, 1]).

The last entry, A, of the RGBA stands for alpha (transparency, 0 means invisible). You may want to set them to higher values if you want to observe the dots easily.

import numpy as np
import matplotlib.pyplot as plt

x = np.array([1, 2])
y = np.array([[2, 3],[1, 4]])

color_rgba = np.array([[255, 0, 0, 1],
                        [0, 255, 0, 1],
                        [0, 0, 255, 1],
                        [255, 215, 0, 1]], dtype=float)

color_rgba[:, :3] = color_rgba[:, :3] / 255

plt.scatter(np.repeat(x, y.shape[1]), y.flat, s=100, c=color_rgba)

plt.show()