How to make a log log histogram in python

Question

Given an an array of values, I want to plot a log log histogram of these values by their counts. I only know how to log the x values, but not the y values because they are not explicitly created in my program.

Solution

Check out the pyplot documentation.

• pyplot.hist can "log" y axis for you with keyword argument log=True
• pyplot.hist accepts bins keyword argument, but you have to "log" x axis yourself

For example:

#!/usr/bin/python
import numpy
from matplotlib import pyplot as plt

data = numpy.random.gumbel(2 ** 20, 2 ** 19, (1000, ))

bins = range(15, 25)
plt.xticks(bins, ["2^%s" % i for i in bins])
plt.hist(numpy.log2(data), log=True, bins=bins)
plt.show()

This will give you the actual counts of how how many elements fall into each bin, plotted on a log axis (which is what people usually mean by a log plot). I couldn't tell from your wording if you wanted this or the log of the count plotted on a linear axis.

Btw., bins don't even have to be spaced evenly.

Comments

[Nikana Reklawyks]

To plot the log of the count of a linear axis is comparatively easier, and anyway both methods give the same graph. +1 for the key beginning. But I don't get what you do in the code : are you displaying fake exponential tick tags on what's really a linear x-scale ?