Python scatter plot 2 dimensional array

Question

I'm trying to do something that I think should be pretty straight forward but I can't seem to get it to work.

I'm trying to plot 16 byte values measured over time to see how they change. I'm trying to use a scatter plot to do this with: x axis being the measurement index y axis being the index of the byte and the color indicating the value of the byte.

I have the data stored in a numpy array where data[2][14] would give me the value of the 14th byte in the 2nd measurement.

Every time I try to plot this, I'm getting either:

ValueError: x and y must be the same size
IndexError: index 10 is out of bounds for axis 0 with size 10

Here is the sample test I'm using:

import numpy
import numpy.random as nprnd
import matplotlib.pyplot as plt

#generate random measurements
# 10 measurements of 16 byte values
x = numpy.arange(10)
y = numpy.arange(16)
test_data = nprnd.randint(low=0,high=65535, size=(10, 16))

#scatter plot the measurements with
# x - measurement index (0-9 in this case)
# y - byte value index (0-15 in this case) 
# c = test_data[x,y]

plt.scatter(x,y,c=test_data[x][y])
plt.show()

I'm sure it is something stupid I'm doing wrong but I can't seem to figure out what.

Thanks for the help.

xnx · Accepted Answer · 2015-05-20 16:09:33Z

13

Try using a meshgrid to define your point locations, and don't forget to index into your NumPy array properly (with [x,y] rather than [x][y]):

x, y = numpy.meshgrid(x,y)
plt.scatter(x,y,c=test_data[x,y])
plt.show()

enter image description here

answered May 20, 2015 at 16:09

xnx

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