Matplotlib in python | connecting dots

Question

What is the possible way to connect dots I needed?

Here is part of my code for you to understand what I mean:

x = [0, 5, 10, 15, 100, 105, 110, 115]
y = [15, 10, 5, 0, 115, 110, 105, 100]
plt.figure(figsize=(5, 5))

plt.xlim(-1, 120)
plt.ylim(-1, 120)
plt.grid()      

plt.plot(x, y, 'og-')

Have this:

But I have to connect those grouped dots from (0, 15) to (15, 0) and (100, 115) to (115, 100) only. I do not need that long connection between the dots: (15, 0) to (100, 115)

Can anyone help find a solution for this problem?

It's not a mind reader. When you give it a series of points, there is no way for it to determine one segment should not be drawn. Separating the segments is YOUR job. — RufusVS
– RufusVS, Commented Oct 8, 2021 at 16:39
Oh, you want to drop lines segments that exceed a certain length. I think there's an answer now. — RufusVS
– RufusVS, Commented Oct 8, 2021 at 20:19

JohanC · Accepted Answer · 2021-10-08 17:17:54Z

2

If you have a very long x-array, you can combine numpy's np.diff with np.nonzero to calculate the indices. np.diff would calculate the subsequent differences, which can be compared to a threshold. np.nonzero will return all indices where the comparison results in True. Looping through these indices lets you draw each part separately.

from matplotlib import pyplot as plt
import numpy as np

x = [0, 5, 10, 15, 100, 105, 110, 115]
y = [15, 10, 5, 0, 115, 110, 105, 100]
threshold = 20
indices = np.nonzero(np.diff(x) >= threshold)[0] + 1

for i0, i1 in zip(np.append(0, indices), np.append(indices, len(x))):
    plt.plot(x[i0:i1], y[i0:i1], '-go')
plt.show()

Here is a more elaborate example:

from matplotlib import pyplot as plt
import numpy as np

N = 30
x = (np.random.randint(1, 5, N) * 5).cumsum()
y = np.random.randint(0, 10, N) * 5
plt.plot(x, y, 'r--') # this is how the complete line would look like
threshold = 20
indices = np.nonzero(np.diff(x) >= threshold)[0] + 1
for i0, i1 in zip(np.append(0, indices), np.append(indices, len(x))):
    plt.plot(x[i0:i1], y[i0:i1], '-go')
plt.show()

answered Oct 8, 2021 at 17:17

JohanC

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user388794 Over a year ago

Thank you, will think about it.

Behdad Abdollahi Moghadam · Accepted Answer · 2021-10-08 16:30:34Z

1

draw the lines you want, and don't draw the ones you don't:

from matplotlib import pyplot as plt
#x = [0, 5, 10, 15, 100, 105, 110, 115]
#y = [15, 10, 5, 0, 115, 110, 105, 100]

plt.figure(figsize=(5, 5))

plt.xlim(-1, 120)
plt.ylim(-1, 120)
plt.grid()   

x1 = [0, 5, 10, 15]
y1 = [15, 10, 5, 0]

x2 = [100, 105, 110, 115]
y2 = [115, 110, 105, 100]


plt.plot(x1, y1, 'og-')
plt.plot(x2,y2, 'og-')

plt.show()

Output:

answered Oct 8, 2021 at 16:30

Behdad Abdollahi Moghadam

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1 Comment

user388794 Over a year ago

Imagine you have a very big array.

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