_how-to-too-many-ticks

Why do I have so many ticks, and/or why are they out of order?

Sometimes Matplotlib will unexpectedly plot with a tick for each data point,

and/or the ticks will be out of numerical order. This is usually a sign that you

have passed in a list of strings rather than a list or array of floats or

datetime objects. This will often happen when reading in a comma-delimited text

file. Matplotlib treats lists of strings as "categorical" variables

(:doc:`/examples/lines_bars_and_markers/categorical_variables`), and by default

puts one tick per "category", and plots them in the order in which they are

supplied.

In the example below, the upper row plots are plotted using strings for *x*;

note that each string gets a tick, and they are in the order of the list passed

to Matplotlib. In the lower row the data is converted to either floats or

datetime64; note that the ticks are now ordered and spaced numerically.

.. plot::

:include-source:

:align: center

import matplotlib.pyplot as plt

import numpy as np

fig, ax = plt.subplots(2, 2, constrained_layout=True, figsize=(6, 6))

x = ['1', '5', '2', '3']

y = [1, 4, 2, 3]

ax[0, 0].plot(x, y, 'd')

ax[0, 0].set_xlabel('Categories')

# convert to numbers:

x = np.asarray(x, dtype='float')

ax[1, 0].plot(x, y, 'd')

ax[1, 0].set_xlabel('Floats')

x = ['2021-10-01', '2021-11-02', '2021-12-03', '2021-10-04']

y = [0, 2, 3, 1]

ax[0, 1].plot(x, y, 'd')

ax[0, 1].tick_params(axis='x', labelrotation=45)

# convert to datetime64

x = np.asarray(x, dtype='datetime64[s]')

ax[1, 1].plot(x, y, 'd')

ax[1, 1].tick_params(axis='x', labelrotation=45)

If *x* has 100 elements, all strings, then we would have 100 (unreadable)

ticks:

.. plot::

import matplotlib.pyplot as plt

import numpy as np

fig, ax = plt.subplots(figsize=(6, 2.5))

x = [f'{xx}' for xx in np.arange(100)]

y = np.arange(100)

ax.plot(x, y)