Plotting lines connecting points

31

I know there is another very similar question, but I could not extract the information I need from it.

plotting lines in pairs

I have 4 points in the (x,y) plane: x=[x1,x2,x3,x4] and y=[y1,y2,y3,y4]

x=[-1 ,0.5 ,1,-0.5]
y=[ 0.5,  1, -0.5, -1]

Now, I can plot the four points by doing:

import matplotlib.pyplot as plt

plt.plot(x,y, 'ro')
plt.axis('equal')
plt.show()

But, apart from the four points, I would like to have 2 lines:

1) one connecting (x1,y1) with (x2,y2) and 2) the second one connecting (x3,y3) with (x4,y4).

This is a simple toy example. In the real case I have 2N points in the plane.

How can I get the desired output: for points with two connecting lines ?

Thank you.

This question is tagged with matplotlib

~ Asked on 2016-02-12 13:08:51

The Best Answer is


51

I think you're going to need separate lines for each segment:

import numpy as np
import matplotlib.pyplot as plt

x, y = np.random.random(size=(2,10))

for i in range(0, len(x), 2):
    plt.plot(x[i:i+2], y[i:i+2], 'ro-')

plt.show()

(The numpy import is just to set up some random 2x10 sample data)

enter image description here

~ Answered on 2016-02-12 13:23:37


17

You can just pass a list of the two points you want to connect to plt.plot. To make this easily expandable to as many points as you want, you could define a function like so.

import matplotlib.pyplot as plt

x=[-1 ,0.5 ,1,-0.5]
y=[ 0.5,  1, -0.5, -1]

plt.plot(x,y, 'ro')

def connectpoints(x,y,p1,p2):
    x1, x2 = x[p1], x[p2]
    y1, y2 = y[p1], y[p2]
    plt.plot([x1,x2],[y1,y2],'k-')

connectpoints(x,y,0,1)
connectpoints(x,y,2,3)

plt.axis('equal')
plt.show()

enter image description here

Note, that function is a general function that can connect any two points in your list together.

To expand this to 2N points, assuming you always connect point i to point i+1, we can just put it in a for loop:

import numpy as np
for i in np.arange(0,len(x),2):
    connectpoints(x,y,i,i+1)

In that case of always connecting point i to point i+1, you could simply do:

for i in np.arange(0,len(x),2):
    plt.plot(x[i:i+2],y[i:i+2],'k-')

~ Answered on 2016-02-12 13:21:55


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