Logscale plots with zero values in matplotlib

Question

I am currently using logscale in order to have greater possibilities of plotting my data. Nevertheless, my data consists also of zero values. I know that these zero values will not work on logscale as log(0) is not defined.

So e.g.,

fig = plt.figure()
ax = fig.add_subplot(111)
ax.plot([0,1,2],[10,10,100],marker='o',linestyle='-')
ax.set_yscale('log')
ax.set_xscale('log')

completely omits the zero value. Is this behavior acceptable? At least there should be some kind of warning. I only recognized it by accident. Is there maybe also a way of plotting zero value data in logscale?

Thanks!

P.S.: I hope this fits to stackoverflow. I did not find a mailing list of matplotlib.

possible duplicate of Matplotlib logarithmic scale with zero value — Benjamin Bannier
– Benjamin Bannier, Commented Jun 3, 2013 at 19:55
@honk - Actually, that question doesn't answer the OP's question. — Joe Kington
– Joe Kington, Commented Jun 3, 2013 at 19:59
@JoeKington: I wasn't aware of symlog which is also a nice answer to the question I linked to. When using it one still needs to keep in mind that the displayed plot isn't strictly a logplot anymore though. — Benjamin Bannier
– Benjamin Bannier, Commented Jun 3, 2013 at 20:13

Community · Accepted Answer · 2017-05-23 10:31:02Z

64

It's easiest to use a "symlog" plot for this purpose. The interval near 0 will be on a linear scale, so 0 can be displayed.

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.plot([0,1,2],[10,10,100],marker='o',linestyle='-')
ax.set_yscale('symlog')
ax.set_xscale('symlog')
plt.show()

enter image description here

Symlog sets a small interval near zero (both above and below) to use a linear scale. This allows things to cross 0 without causing log(x) to explode (or go to -inf, rather).

There's a nice visual comparison as an SO answer here: https://stackoverflow.com/a/3513150/325565

edited May 23, 2017 at 10:31

CommunityBot

11 silver badge

answered Jun 3, 2013 at 20:00

Joe Kington

287k73 gold badges621 silver badges474 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

fsociety Over a year ago

Great answer. Thanks for that. Could you elaborate what symlog is exactly doing?

Joe Kington Over a year ago

Sure! See the updates. There are also a few examples in the matplotlib gallery (e.g. matplotlib.org/examples/pylab_examples/symlog_demo.html ), but they're not as clear as the SO answer I linked to.

Collectives™ on Stack Overflow

Logscale plots with zero values in matplotlib

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related