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Simplify the LineCollection example #27873

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85 changes: 37 additions & 48 deletions galleries/examples/shapes_and_collections/line_collection.py
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Expand Up @@ -3,79 +3,68 @@
Plotting multiple lines with a LineCollection
=============================================

Matplotlib can efficiently draw multiple lines at once using a
`~.LineCollection`, as showcased below.
Matplotlib can efficiently draw multiple lines at once using a `~.LineCollection`.
"""

import matplotlib.pyplot as plt
import numpy as np

from matplotlib.collections import LineCollection

x = np.arange(100)
# Here are many sets of y to plot vs. x
ys = x[:50, np.newaxis] + x[np.newaxis, :]
colors = ["indigo", "blue", "green", "yellow", "orange", "red"]

segs = np.zeros((50, 100, 2))
segs[:, :, 1] = ys
segs[:, :, 0] = x
# create a list of half-circles with varying radii
theta = np.linspace(0, np.pi, 36)
radii = np.linspace(4, 5, num=len(colors))
arcs = [np.column_stack([r * np.cos(theta), r * np.sin(theta)]) for r in radii]

# Mask some values to test masked array support:
segs = np.ma.masked_where((segs > 50) & (segs < 60), segs)
fig, ax = plt.subplots(figsize=(6.4, 3.2))
# set axes limits manually because Collections do not take part in autoscaling
ax.set_xlim(-6, 6)
ax.set_ylim(0, 6)
ax.set_aspect("equal") # to make the arcs look circular

# We need to set the plot limits, they will not autoscale
fig, ax = plt.subplots()
ax.set_xlim(x.min(), x.max())
ax.set_ylim(ys.min(), ys.max())
# create a LineCollection with the half-circles
# its properties can be set per line by passing a sequence (here used for *colors*)
# or they can be set for all lines by passing a scalar (here used for *linewidths*)
line_collection = LineCollection(arcs, colors=colors, linewidths=4)
ax.add_collection(line_collection)

# *colors* is sequence of rgba tuples.
# *linestyle* is a string or dash tuple. Legal string values are
# solid|dashed|dashdot|dotted. The dash tuple is (offset, onoffseq) where
# onoffseq is an even length tuple of on and off ink in points. If linestyle
# is omitted, 'solid' is used.
# See `matplotlib.collections.LineCollection` for more information.
colors = plt.rcParams['axes.prop_cycle'].by_key()['color']

line_segments = LineCollection(segs, linewidths=(0.5, 1, 1.5, 2),
colors=colors, linestyle='solid')
ax.add_collection(line_segments)
ax.set_title('Line collection with masked arrays')
plt.show()

# %%
# In the following example, instead of passing a list of colors
# (``colors=colors``), we pass an array of values (``array=x``) that get
# colormapped.
# Instead of passing a list of colors (``colors=colors``), we can alternatively use
# colormapping. The lines are then color-coded based on an additional array of values
# passed to the *array* parameter. In the below example, we color the lines based on
# their radius by passing ``array=radii``.

N = 50
x = np.arange(N)
ys = [x + i for i in x] # Many sets of y to plot vs. x
segs = [np.column_stack([x, y]) for y in ys]
num_arcs = 15
theta = np.linspace(0, np.pi, 36)
radii = np.linspace(4, 5.5, num=num_arcs)
arcs = [np.column_stack([r * np.cos(theta), r * np.sin(theta)]) for r in radii]

fig, ax = plt.subplots()
ax.set_xlim(np.min(x), np.max(x))
ax.set_ylim(np.min(ys), np.max(ys))
fig, ax = plt.subplots(figsize=(6.4, 3))
# set axes limits manually because Collections do not take part in autoscaling
ax.set_xlim(-6, 6)
ax.set_ylim(0, 6)
ax.set_aspect("equal") # to make the arcs look circular

line_segments = LineCollection(segs, array=x,
linewidths=(0.5, 1, 1.5, 2),
linestyles='solid')
ax.add_collection(line_segments)
axcb = fig.colorbar(line_segments)
axcb.set_label('Line Number')
ax.set_title('Line Collection with mapped colors')
plt.sci(line_segments) # This allows interactive changing of the colormap.
plt.show()
# create a LineCollection with the half-circles and color mapping
line_collection = LineCollection(arcs, array=radii, cmap="rainbow")
ax.add_collection(line_collection)

fig.colorbar(line_collection, label="Radius")
ax.set_title("Line Collection with mapped colors")

plt.show()
# %%
#
# .. admonition:: References
#
# The use of the following functions, methods, classes and modules is shown
# in this example:
#
# - `matplotlib.collections`
# - `matplotlib.collections.LineCollection`
# - `matplotlib.cm.ScalarMappable.set_array`
# - `matplotlib.collections.Collection.set_array`
# - `matplotlib.axes.Axes.add_collection`
# - `matplotlib.figure.Figure.colorbar` / `matplotlib.pyplot.colorbar`
# - `matplotlib.pyplot.sci`