Plotting a list of (x, y) coordinates in python matplotlib

Question

I have a list of pairs (a, b) that I would like to plot with matplotlib in python as actual x-y coordinates. Currently, it is making two plots, where the index of the list gives the x-coordinate, and the first plot's y values are the as in the pairs and the second plot's y values are the bs in the pairs.

To clarify, my data looks like this: li = [(a,b), (c,d), ... , (t, u)] I want to do a one-liner that just calls plt.plot() incorrect. If I didn't require a one-liner I could trivially do:

xs = [x[0] for x in li]
ys = [x[1] for x in li]
plt.plot(xs, ys)

How can I get matplotlib to plot these pairs as x-y coordinates?

Solution 1

As per this example:

import numpy as np
import matplotlib.pyplot as plt

N = 50
x = np.random.rand(N)
y = np.random.rand(N)

plt.scatter(x, y)
plt.show()

will produce:

To unpack your data from pairs into lists use zip:

x, y = zip(*li)

So, the one-liner:

plt.scatter(*zip(*li))

Solution 2

If you have a numpy array you can do this:

import numpy as np
from matplotlib import pyplot as plt

data = np.array([
    [1, 2],
    [2, 3],
    [3, 6],
])
x, y = data.T
plt.scatter(x,y)
plt.show()

Solution 3

If you want to plot a single line connecting all the points in the list

plt.plot(li[:])

plt.show()

This will plot a line connecting all the pairs in the list as points on a Cartesian plane from the starting of the list to the end. I hope that this is what you wanted.

Comments

[denis]

For a 2-column numpy array, plt.scatter( * xy.T ) works: short and obscure for x, y = xy.T; plt.scatter( x, y )

[Dartmouth]

He didn't want to plot a single line, he wanted to plot with a "one-liner" (a single line of code). The answer he was looking for (and got 3 years ago) was to use scatter().

[Gathide]

Since this answer states the condition under which it works i.e. "If you want to plot a single line connecting all the points in the list", does it really deserve a down vote?

[Trevor Boyd Smith]

x, y = zip(*li) is really elegant python code! i've been doing the more straight-forward two lines of code with a list compression on each line (like the original question)

[Max Coplan]

So there is no way to have a np.array of data=np.array([[x1,y1],[x2,y2],etc.]) and using plt.plot(data). I'll always have to give two arrays instead of arrays of arrays?

[Zweedeend]

@MaxCoplan, that's right, but you could use plt.plot(*data.T) which does the same as the above but skips the intermediate step.

[jamesdlin]

It's kind of confusing what the random plt.scatter example has to do with the question.

[Eric Duminil]

@Gathide: Yes, it deserves a downvote, since it doesn't work at all, and doesn't fit the description. plt.plot(li) is just like plt.plot(li[:]). It simply plots 2 lines, using the pairs as (y1, y2) and not as (x1, y1).