Plot logarithmic axes with matplotlib in python

I want to plot a graph with one logarithmic axis using matplotlib.

I've been reading the docs, but can't figure out the syntax. I know that it's probably something simple like 'scale=linear' in the plot arguments, but I can't seem to get it right

Sample program:

import pylab import matplotlib.pyplot as plt a = [pow(10, i) for i in range(10)] fig = plt.figure() ax = fig.add_subplot(2, 1, 1) line, = ax.plot(a, color='blue', lw=2) pylab.show() 

6 Answers

You can use the Axes.set_yscale method. That allows you to change the scale after the Axes object is created. That would also allow you to build a control to let the user pick the scale if you needed to.

The relevant line to add is:

ax.set_yscale('log') 

You can use 'linear' to switch back to a linear scale. Here's what your code would look like:

import pylab import matplotlib.pyplot as plt a = [pow(10, i) for i in range(10)] fig = plt.figure() ax = fig.add_subplot(2, 1, 1) line, = ax.plot(a, color='blue', lw=2) ax.set_yscale('log') pylab.show() 

First of all, it's not very tidy to mix pylab and pyplot code. What's more, pyplot style is preferred over using pylab.

Here is a slightly cleaned up code, using only pyplot functions:

from matplotlib import pyplot a = [ pow(10,i) for i in range(10) ] pyplot.subplot(2,1,1) pyplot.plot(a, color='blue', lw=2) pyplot.yscale('log') pyplot.show() 

The relevant function is pyplot.yscale(). If you use the object-oriented version, replace it by the method Axes.set_yscale(). Remember that you can also change the scale of X axis, using pyplot.xscale() (or Axes.set_xscale()).

Check my question What is the difference between ‘log’ and ‘symlog’? to see a few examples of the graph scales that matplotlib offers.

You simply need to use semilogy instead of plot:

from pylab import * import matplotlib.pyplot as pyplot a = [ pow(10,i) for i in range(10) ] fig = pyplot.figure() ax = fig.add_subplot(2,1,1) line, = ax.semilogy(a, color='blue', lw=2) show() 

if you want to change the base of logarithm, just add:

plt.yscale('log',base=2) 

Before Matplotlib 3.3, you would have to use basex/basey as the bases of log

I know this is slightly off-topic, since some comments mentioned the ax.set_yscale('log') to be "nicest" solution I thought a rebuttal could be due. I would not recommend using ax.set_yscale('log') for histograms and bar plots. In my version (0.99.1.1) i run into some rendering problems - not sure how general this issue is. However both bar and hist has optional arguments to set the y-scale to log, which work fine.

references:

So if you are simply using the unsophisticated API, like I often am (I use it in ipython a lot), then this is simply

yscale('log') plot(...) 

Hope this helps someone looking for a simple answer! :).