Connect points with horizontal lines

Question

The goal is to fill the space between two arrays y1 and y2, similar to matplotlib\'s fill_between. But I don\'t want to fill the space with a polyg

Answer 1

I wrote a little function which takes two arrays y1, y2 (x1, x2 are optional) and connects their data points vertically.

def draw_lines_between(*, ax, x1=None, x2=None, y1, y2, color_list=None, **kwargs):
    assert len(y1) == len(y2)
    assert isinstance(color_list, list)

    n = len(y1)
    if x1 is None:
        x1 = np.arange(n)
    if x2 is None:
        x2 = x1

    if color_list is None:
        color_list = [None for i in range(n)]
    elif len(color_list) < n:
        color_list = [color_list] * n

    h = np.zeros(n, dtype=object)
    for i in range(n):
        h[i] = ax.plot((x1[i], x2[i]), (y1[i], y2[i]), color=color_list[i], **kwargs)[0]

    return h


import matplotlib.pyplot as plt
import numpy as np

n = 10
y1 = np.random.random(n)
y2 = np.random.random(n) + 1
x1 = np.arange(n)
color_list = [str(x) for x in np.round(np.linspace(0., 0.8, n), 2)]

fig, ax = plt.subplots()
ax.plot(x1, y1, 'r')
ax.plot(x1, y2, 'b')
draw_lines_between(ax=ax, x1=x1, y1=y1, y2=y2, color_list=color_list)

Answer 2

Using a LineCollection could be handy if there are lots of lines in the game. Similar to the other answer, but less expensive:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.collections import LineCollection

def draw_lines_between(*, x1=None, x2=None, y1, y2, ax=None, **kwargs):
    ax = ax or plt.gca()
    x1 = x1 if x1 is not None else np.arange(len(y1))
    x2 = x2 if x2 is not None else x1

    cl = LineCollection(np.stack((np.c_[x1, x2], np.c_[y1, y2]), axis=2), **kwargs)
    ax.add_collection(cl)
    return cl

n = 10
y1 = np.random.random(n)
y2 = np.random.random(n) + 1
x = np.arange(n)
color_list = [str(x) for x in np.round(np.linspace(0., 0.8, n), 2)]

fig, ax = plt.subplots()
ax.plot(x, y1, 'r')
ax.plot(x, y2, 'b')
draw_lines_between(ax=ax, x1=x, y1=y1, y2=y2, colors=color_list)

plt.show()