Question

I’m using matplotlib and Python 2.7

I have a MxN matrix of tuples, an x-coordinate and a speed. How do I plot M rows of points with N points in each row at the specified x-coordiantes? Preferrably with the first row at the top?

I’ve tried various examples from the documentation but honestly I haven’t really found anything.

Here is a rough example of what I want to accomplish, the t-coordinate goes from 0 to M, the x range has a fixed size. The dots are placed in a horizintal line according to their values. Is it somewhat readable?

Answer 1

It sounds like you have something like this:

import numpy as np
import matplotlib.pyplot as plt

x = np.random.random((10, 20))
x = x.cumsum(axis=1)

fig, ax = plt.subplots()
for i, row in enumerate(x):
    ax.plot(row, i * np.ones_like(row), 'ko')

ax.set_ylim([-0.5, 9.5])
ax.set_yticks(range(10))
ax.invert_yaxis()
plt.show()

Edit:

@EMS is quite right, I missed a rather key point of your question.

However, if you have nested lists of tuples, just convert it to an array. It will be a 3D array that you can slice as you need for the x-position and velocity. There’s absolutely no need to generate a second dataset, and matplotlib will convert whatever you input to it into a numpy array regardless, so there’s no performance penalty.

E.g.

import numpy as np

data = [[(1, 2), (3, 4)],
        [(5, 6), (7, 8)]]

data = np.array(data)

x = data[:,:,0]
velocity = data[:,:,1]

This yields:

x: 
array([[1, 3],
       [5, 7]])

velocity:
array([[2, 4],
       [6, 8]])