Line with dashes of multiple colours

Question

I want to plot a line with dashes of different colours. Here is my current solution:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection
from matplotlib.colors import ListedColormap, BoundaryNorm

def plotmulticolor(x, y, cmap, axis, dashes=100):

    norm = BoundaryNorm(np.arange(cmap.N + 1) - 0.5, cmap.N)
    xp = []
    yp = []
    cp = []

    for i in range(len(x) - 1):
        xi = [x[i], x[i + 1]]
        yi = [y[i], y[i + 1]]
        d = np.sqrt(np.diff(ax.transLimits.transform(xi)) ** 2 + np.diff(ax.transLimits.transform(yi)) ** 2)
        n = int(d / np.sqrt(2) * dashes)
        xp += np.linspace(xi[0], xi[1], n).tolist()
        yp += np.linspace(yi[0], yi[1], n).tolist()
        cp += np.tile(np.arange(cmap.N), int(np.ceil(n / cmap.N)))[:n - 1].tolist()

    points = np.array([xp, yp]).T.reshape(-1, 1, 2)
    segments = np.concatenate([points[:-1], points[1:]], axis=1)
    lc = LineCollection(segments, cmap=cmap, norm=norm)
    lc.set_array(np.array(cp))
    return ax.add_collection(lc)

fig, ax = plt.subplots()
ax.set_xlim([0, 10])
ax.set_ylim([0, 10])
plotmulticolor([0, 5, 10], [0, 1, 10], ListedColormap(["r", "b", "g"]), axis=ax)
plt.show()

which gives what I want:

The problem is however that I hand-compute the number of dashes, which is heuristic, but mostly problematic as it requires a choice of appropriate scale. Currently I assume that I set the axes limits before, which gives me a scale, and I compute the dash size from it.

My question now is: is there a cleverer way that avoids the somewhat heuristic computation of the dash-size?

Line with dashes of multiple colours

0 Answers