获取 python 中正方形边缘的随机点

Question

Question

Given a plotting window, how does one generate random points at the perimeter of a square (perimeter of the plotting window)?

Background and attempt

I found a similar question with regards to a rectangle in javascript .

I managed to write a program to generate random points within limits but the question is regarding how one could find random points with the condition that they are at the edge of the plot (either x is equal to 5 or -5,or y is equal to 5 or -5 in this case).

import numpy as np
import matplotlib.pyplot as plt

# Parameters
n = 6 # number of points
a = 5 # upper bound
b = -5 # lower bound

# Random coordinates [b,a) uniform distributed
coordy = (b - a) *  np.random.random_sample((n,)) + a # generate random y
coordx = (b - a) *  np.random.random_sample((n,)) + a # generate random x

# Create limits (x,y)=((-5,5),(-5,5))
plt.xlim((b,a))
plt.ylim((b,a))

# Plot points
for i in range(n):
    plt.plot(coordx[i],coordy[i],'ro')

plt.show()

Summary

So to summarize, my question is how do I generate random coordinates given that they are at the edge of the plot/canvas. Any advice or help will be appreciated.

Answer 1

One possible approach (despite not very elegant) is the following: divide horizontal and vertical points Suppose you want to draw a point at the top or at the bottom of the window. Then,

1. Select randomly the y coordinate as b or - b
2. Select randomly (uniform distribution) the x coordinate

Similar approach for right and left edges of the window.

Hope that helps.

Answer 2

You could use this, but this is assuming you want to discard them when it is found they aren't on the edge.

for x in coordx:
    if x != a:
        coordx.pop(x)
    else:
        continue

And then do the same for y.

Answer 3

Here's a way to do that:

import numpy as np
import matplotlib.pyplot as plt

# Parameters
n = 6 # number of points
a = 5 # upper bound
b = -5 # lower bound

# Random coordinates [b,a) uniform distributed
coordy = (b - a) *  np.random.random_sample((n,)) + a # generate random y
coordx = (b - a) *  np.random.random_sample((n,)) + a # generate random x

# This is the new code
reset_axis = np.random.choice([True, False], n) # select which axis to reset
reset_direction = np.random.choice([a,b], n) # select to go up / right or down / left

coordx[reset_axis] = reset_direction[reset_axis]
coordy[~reset_axis] = reset_direction[~reset_axis]
# end of new code. 

# Create limits (x,y)=((-5,5),(-5,5))
plt.xlim((b,a))
plt.ylim((b,a))

# Plot points
for i in range(n):
    plt.plot(coordx[i],coordy[i],'ro')

plt.show()

The result is:

Answer 4

Here is what you can do:

from random import choice
import matplotlib.pyplot as plt
from numpy.random import random_sample

n = 6
a = 5
b = -5

plt.xlim((b,a))
plt.ylim((b,a))

for i in range(n):
    r = (b - a) * random_sample() + a
    random_point = choice([(choice([a,b]), r),(r, choice([a,b]))])
    plt.scatter(random_point[0],random_point[1])

plt.show()

Output:

Answer 5

Geometrically speaking, being on the edge requires that a point satisfy certain conditions. Assuming that we are talking about a grid whose dimensions are defined by x ~ [0, a] and y ~ [0, b] :

• The y-coordinate is either 0 or b , with the x-coordinate within [0, a] , or
• The x-coordinate is either 0 or a , with the y-coordinate within [0, b]

There are obviously more than one way to go about this, but here is a simple method to get you started.

def plot_edges(n_points, x_max, y_max, x_min=0, y_min=0):
    # if x_max - x_min = y_max - y_min, plot a square
    # otherwise, plot a rectangle

    vertical_edge_x = np.random.uniform(x_min, x_max, n_points)
    vertical_edige_y = np.asarray([y_min, y_max])[
        np.random.randint(2, size=n_points)
    ]
    horizontal_edge_x = np.asarray([x_min, x_max])[
        np.random.randint(2, size=n_points)
    ]
    horizontal_edge_y = np.random.uniform(x_min, x_max, n_points)

    # plot generated points
    plt.scatter(vertical_edge_x, vertical_edige_y)
    plt.scatter(horizontal_edge_x, horizontal_edge_y)
    plt.show()

Answer 6

Can you try this out?

import numpy as np
import matplotlib.pyplot as plt

# Parameters
n = 6 # number of points
a = 5 # upper bound
b = -5 # lower bound

import random

coordx,coordy=[],[]
for i in range(n):
    xy = random.choice(['x','y'])
    if xy=='x':
        coordx.append(random.choice([b,a])) # generate random x
        coordy.append(random.random()) # generate random y
    if xy=='y':
        coordx.append(random.random()) # generate random x
        coordy.append(random.choice([b,a])) # generate random y

# Create limits (x,y)=((-5,5),(-5,5))
plt.xlim((b,a))
plt.ylim((b,a))

# Plot points
for i in range(n):
    plt.plot(coordx[i],coordy[i],'ro')

plt.show()

Here is a sample output: