CODEWITHSUNDEEP
pythonmatplotlib
ZK Zhao
ZK Zhao

Reputation: 21533

Python & Matplot: How can I draw a simple shape by points?

I just want to draw simple shape by points, like this:

import matplotlib.pyplot as plt

rectangle = [(0,0),(0,1),(1,1),(1,0)]
hexagon = [(0,0),(0,1),(1,2),(2,1),(2,0),(1,-1)]
l_shape = [(0,0),(0,3),(1,3),(1,1),(3,1),(3,0)]
concave = [(0,0),(0,3),(1,3),(1,1),(2,1),(2,3),(3,3),(3,0)]

for points in [rectangle, hexagon, l_shape, concave]:
    # 1. Can I get rid of the zip? plot directly by points 
    # 2. How can I make the shape complete?
    xs, ys = zip(*points)
    plt.plot(xs, ys, 'o')
    plt.plot(xs, ys, '-')

    automin, automax = plt.xlim()
    plt.xlim(automin-0.5, automax+0.5)
    automin, automax = plt.ylim()
    plt.ylim(automin-0.5, automax+0.5)
    # Can I display the shapes 2 in 1 line?
    plt.show()

My question is enter image description here

  1. How can I get rid of the *zip? I mean, directyly draw by points, rather than 2 array.
  2. How to make these shapes complete? Since I'm looping through all the points, the first and last cannot connect together, how can I do it?
  3. Can I draw the shape without giving the specific points order?(Something like convex hull?)

Upvotes: 6

Views: 8476

Answers (2)

Konstantin
Konstantin

Reputation: 25339

The code below doesn't use temporary variables xs and ys, but a direct tuple unpacking. Also I add first point from points list to make shapes complete.

rectangle = [(0,0),(0,1),(1,1),(1,0)]
hexagon = [(0,0),(0,1),(1,2),(2,1),(2,0),(1,-1)]
l_shape = [(0,0),(0,3),(1,3),(1,1),(3,1),(3,0)]
concave = [(0,0),(0,3),(1,3),(1,1),(2,1),(2,3),(3,3),(3,0)]

for points in [rectangle, hexagon, l_shape, concave]:
    plt.plot(*zip(*(points+points[:1])), marker='o')

    automin, automax = plt.xlim()
    plt.xlim(automin-0.5, automax+0.5)
    automin, automax = plt.ylim()
    plt.ylim(automin-0.5, automax+0.5)

    plt.show()

Provide this answer as an alternative leekaiinthesky's post

Upvotes: 1

leekaiinthesky
leekaiinthesky

Reputation: 5593

To close the shape, just add the first point again at the end of the list:

# rectangle = [(0,0),(0,1),(1,1),(1,0)]
rectangle = [(0,0),(0,1),(1,1),(1,0),(0,0)]

plt.plot takes a list of x coordinates and a list of y coordinates. I would say that the way you're doing it now is already the way of doing it "by points rather than 2 arrays". Because if you wanted to do it without zip, it would look like this:

rectangleX = [0, 0, 1, 1, 0]
rectangleY = [0, 1, 1, 0, 0]
plt.plot(rectangleX, rectangleY, 'o')
plt.plot(rectangleX, rectangleY, '-')

Update:

For better polygon support, use the patches module [example]. This may be more along the lines of what you're looking for. By default (closed = True), it will close the path for you, and it also allows you to add vertices directly to a list (not two separate lists):

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches

rectangle = [(0,0),(0,1),(1,1),(1,0)]

fig, ax = plt.subplots()
ax.add_patch(mpatches.Polygon(rectangle))

automin, automax = plt.xlim()
plt.xlim(automin-0.5, automax+0.5)
automin, automax = plt.ylim()
plt.ylim(automin-0.5, automax+0.5)
plt.show()

Upvotes: 3

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