Unable to reverse xticks inside matplotlib subplot

Question

I have designed a subplot using matplotlib. I am trying to reverse the xticks of the plot. Please see the sample code-

import numpy as np
import matplotlib.pyplot as plt

# generate the data
n = 6
y = np.random.randint(low=0, high=10, size=n)
x = np.arange(n)

# generate the ticks and reverse it
xticks = range(n)
xticks.reverse()

# plot the data
plt.figure()
ax = plt.subplot(111)
ax.bar(x, y)
print xticks # prints [5, 4, 3, 2, 1, 0]
ax.set_xticks(xticks)
plt.show()

Please see below the generated plot-

Please pay attention to the xticks. Even though, ax.set_xticks(xticks) is used but the xticks haven't changed. Am I missing some function call to rerender the plot?

Below is the system information-

matplotlib.__version__
'2.1.1'

matplotlib.__version__numpy__
'1.7.1'

python --version
Python 2.7.15rc1

Please note that I just want to reverse the ticks and do not want to invert axis.

Answer 1

With ax.set_xticks, you are currently specifying tick positions which is invariant to the order of the list. Either you pass [0, 1, 2, 3, 4, 5] or you pass [5, 4, 3, 2, 1, 0]. The difference will not be noticed in the ticks. What you instead want is to have reversed ticklabels for which you should do set_xticklabels(xticks[::-1]). There are two ways to do it:

Way 1

Use plt.xticks where the first argument specifies the location of the ticks and the second arguments specifies the respective ticklabels. Specifically, xticks will provide the tick positions and xticks[::-1] will label your plot with reversed ticklabels.

xticks = range(n)

# plot the data
plt.figure()
ax = plt.subplot(111)
ax.bar(x, y)

plt.xticks(xticks, xticks[::-1])

Way 2 using ax where you need set_xticklabels to get what you want

ax.set_xticks(xticks)
ax.set_xticklabels(xticks[::-1])

Answer 2

Use:

# generate the data
n = 6
y = np.random.randint(low=0, high=10, size=n)
x = np.arange(n)

# generate the ticks and reverse it
xticks = range(n)
# xticks.reverse()

# plot the data
plt.figure()
ax = plt.subplot(111)
ax.bar(x, y)
# print xticks # prints [5, 4, 3, 2, 1, 0]
ax.set_xticklabels(xticks[::-1])          # <- Changed
plt.show()