How to plot lines between points, and change their color based on specific values in Python?

Question

Context:

3x35 values array that associates 1 value per segment
4x35x2 matpos array that gathers the coordinates of 4x35 points (hence 3x35 segments).

Question:

How can I define each segment's color based on their values from the values array ?

Code attempt:

# Array of values for each point
values = np.random.rand(3,35)

# Generate array of positions
x = np.arange(0,35)
y = np.arange(0,4)
matpos = np.array([[(y[i], x[j]) for j in range(0,len(x))] for i in range(0,len(y))])

# plot the figure
plt.figure()
for i in range(len(y)-1):
    for j in range(len(x)):

        # plot each segment
        plt.plot(matpos[i:i+2,j,0],matpos[i:i+2,j,1]) #color = values[i,j]

Michael Cao · Accepted Answer · 2023-02-08 22:31:07Z

1

If your values are just along a grid, you might as well just use plt.imshow(values).

Updated code for desired result:

import matplotlib as mpl
import matplotlib.pyplot as plt
import numpy as np

# Array of values for each point
values = np.random.rand(3,35)

# Transform value to colors depending on colormap
color_norm = mpl.colors.Normalize(np.min(values), np.max(values))

color_map = mpl.cm.get_cmap('viridis')

colors = color_map(color_norm(values))

plt.close('all')

plt.figure()

for (y, x), value in np.ndenumerate(values):

    
    plt.plot([x, x+1], [y, y], c = colors[y,x], linewidth = 10)

edited Feb 8, 2023 at 22:31

answered Feb 8, 2023 at 21:34

Michael Cao

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5 Comments

Nihilum Over a year ago

I want them as lines because they are superimposed on a map

Michael Cao Over a year ago

Ah, I see, and you want each line segment of each line to be colored according to your value?

Nihilum Over a year ago

Yes, exactly ! I know how to do that with scatterplot, but not with plot. And I couldn't find a way to plot segments with scatterplot.

Michael Cao Over a year ago

This would require a bunch of Line2D segments, I believe.

Michael Cao Over a year ago

@Nihilum, I've updated the answer for what you want. The main thing is learning to normalize your values to 0 to 1 for a colormap.

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