CODEWITHSUNDEEP
pythonmatplotlibmatriximshow
strugglinggrad
strugglinggrad

Reputation: 47

Create density plot from 2d matrix

I have a 2d matrix of values which I would like to plot as a 2d histogram.

A simplified example: I have a 1d array of initial velocities, say vi = [1, 2, 3], and for each value in vi, I have a row of corresponding final velocities stored in a 2d array, vf = [ [0.7, 1.1, 1.5], [1.8, 2.1, 2.4], [2.7, 2.9, 3.1] ]. I want to be able to make a 2d histogram of the points (vi, vf), i.e., the coordinates [1, 0.7], [1, 1.1], [1, 1.5], [2, 1.8], [2, 2.1], [2, 2.4], and [3,2.7], [3, 2.9], [3, 3.1].

Is there a way to create such parings?

The answer to this question advises to use imshow or matshow, but that colors bins by the value assigned to each element. What I need is a plotting routine that takes a 2d matrix, divides it into a grid, and colors each bin by the count in each bin.

Any help is appreciated!

Upvotes: 0

Views: 960

Answers (1)

JohanC
JohanC

Reputation: 80329

You seem to have a 2D space, where the x-values come from vi and the y-values from vf. Repeating vi n times (with n the row-length of vf) makes the x and y arrays have the same number of elements, corresponding to the desired tuples.

In code:

import numpy as np
import seaborn as sns
from matplotlib import pyplot as plt

vi = np.array([1, 2, 3])
vf = np.array([[0.7, 1.1, 1.5], [1.8, 2.1, 2.4], [2.7, 2.9, 3.1]])

x = np.repeat(vi, vf.shape[1]) # repeat the x-values by the row-length of `vf`
y = vf.ravel() # convert to a 1D array
sns.histplot(x=x, y=y)
plt.show()

With so little data, the plot looks quite uninteresting. You'll have to test with the real data to find out whether it is what you're expecting.

print([*zip(x,y)]) prints (x,y) as tuples, i.e.

[(1, 0.7), (1, 1.1), (1, 1.5), (2, 1.8), (2, 2.1), (2, 2.4), (3, 2.7), (3, 2.9), (3, 3.1)]

Upvotes: 1

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