Matplotlib - pyplot incorrectly setting axes ticks when using scatter()

Question

I am trying to customize the xticks and yticks for my scatterplot with the simple code below:

import numpy as np
import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(1,1,1)

y_ticks = np.arange(10, 41, 10)
x_ticks = np.arange(1000, 5001, 1000)

ax.set_yticks(y_ticks)
ax.set_xticks(x_ticks)

ax.scatter(some_x, some_y)

plt.show()

If we comment out the line: ax.scatter(x, y), we get an empty plot with the correct result:

However if the code is run exactly as shown, we get this:

Finally, if we run the code with ax.set_yticks(yticks) and ax.set_xticks(xticks) commented out, we also get the correct result (just with the axes not in the ranges I desire them to be):

Note that I am using Python version 2.7. Additionally, some_x and some_y are omitted.

Any input on why the axes are changing in such an odd manner only after I try plotting a scatterplot would be appreciated.

EDIT:

If I run ax.scatter(x, y) before xticks and yticks are set, I get odd results that are slightly different than before:

What happens if you move ax.scatter(x, y) before setting the ticks? — DavidG
– DavidG, Commented Jan 22, 2018 at 23:46
@DavidG I get slightly different results which are still incorrect, and will add to the post (Edited: incorrectly changed the code) — kshah
– kshah, Commented Jan 22, 2018 at 23:50
Please read and understand minimal reproducible example. Most of your trouble comes from using incorrect data, but you do not show the data being used. — ImportanceOfBeingErnest
– ImportanceOfBeingErnest, Commented Jan 23, 2018 at 0:00

ImportanceOfBeingErnest · Accepted Answer · 2018-01-22 23:55:29Z

3

Matplotlib axes will always adjust themselves to the content. This is a desirable feature, because it allows to always see the plotted data, no matter if it ranges from -10 to -9 or from 1000 to 10000.

Setting the xticks will only change the tick locations. So if you set the ticks to locations between -10 and -9, but then plot data from 1000 to 10000, you would simply not see any ticks, because they do not lie in the shown range.

If the automatically chosen limits are not what you are looking for, you need to set them manually, using ax.set_xlim() and ax.set_ylim().

Finally it should be clear that in order to have correct numbers appear on the axes, you need to actually use numbers. If some_x and some_y in ax.scatter(some_x, some_y) are strings, they will not obey to any reasonable limits, but simply be plotted one after the other.

answered Jan 22, 2018 at 23:55

ImportanceOfBeingErnest

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2 Comments

kshah Over a year ago

I was about to post the values of some_x and some_y only to realize that some_y for some reason contained floats enclosed in quotes (i.e. they were actually strings). They were plotted correctly, until I tried changing the axes, which is why I never thoroughly checked!

ImportanceOfBeingErnest Over a year ago

In the future, please check such things before asking a question here, such that any question will contain a minimal reproducible example.

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