How to change the position of some x axis tick labels on top of the bottom x axis in matplotlib? - matplotlib

Question

This is my current script:
#!/usr/bin/env python3
import math
import numpy as np
import matplotlib
import matplotlib.pyplot as plt
"""
Setup for a typical explanatory-style illustration style graph.
"""
h = 2
x = np.linspace(-np.pi, np.pi, 100)
y = 2 * np.sin(x)
rc = {
# Tick in the middle of the axis line.
'xtick.direction' : 'inout',
'ytick.direction' : 'inout',
# Bold is easier to read when we have few ticks.
'font.weight': 'bold',
'xtick.labelbottom': False,
'xtick.labeltop': True,
}
with plt.rc_context(rc):
fig, ax = plt.subplots()
ax.plot(x, y)
ax.set_title(
'2 sin(x), not $\\sqrt{2\\pi}$',
# TODO make LaTeX part bold?
# https://stackoverflow.com/questions/14324477/bold-font-weight-for-latex-axes-label-in-matplotlib
fontweight='bold',
# Too close otherwise.
# https://stackoverflow.com/questions/16419670/increase-distance-between-title-and-plot-in-matplolib/56738085
pad=20
)
# Custom visible plot area.
# ax.set_xlim(-3, 3)
ax.set_ylim(-2.5, 2.5)
# Axes
# Axes on center:
# https://stackoverflow.com/questions/31556446/how-to-draw-axis-in-the-middle-of-the-figure
ax.spines['left'].set_position('zero')
ax.spines['right'].set_visible(False)
ax.spines['bottom'].set_position('zero')
ax.spines['top'].set_visible(False)
# Axes with arrow:
# https://stackoverflow.com/questions/33737736/matplotlib-axis-arrow-tip
ax.plot(1, 0, ls="", marker=">", ms=10, color="k",
transform=ax.get_yaxis_transform(), clip_on=False)
ax.plot(0, 1, ls="", marker="^", ms=10, color="k",
transform=ax.get_xaxis_transform(), clip_on=False)
# Ticks
ax.xaxis.set_ticks_position('bottom')
ax.yaxis.set_ticks_position('left')
# Make ticks a bit longer.
ax.tick_params(width=1, length=10)
# Select tick positions
# https://stackoverflow.com/questions/12608788/changing-the-tick-frequency-on-x-or-y-axis-in-matplotlib
xticks = np.arange(math.ceil(min(x)), math.floor(max(x)) + 1, 1)
yticks = np.arange(math.ceil(min(y)) - 1, math.floor(max(y)) + 2, 1)
# Remove 0.
xticks = np.setdiff1d(xticks, [0])
yticks = np.setdiff1d(yticks, [0])
ax.xaxis.set_ticks(xticks)
ax.yaxis.set_ticks(yticks)
# Another approach. But because I want to be able to remove the 0,
# anyways, I just explicitly give all ticks instead.
# ax.xaxis.set_major_locator(matplotlib.ticker.MultipleLocator(1.0))
# ax.yaxis.set_major_locator(matplotlib.ticker.MultipleLocator(1.0))
# Annotations.
ax.plot([0, np.pi/2], [h, h], '--r')
ax.plot([np.pi/2, np.pi/2], [h, 0], '--r')
ax.plot(np.pi/2, h, marker='o', linewidth=2, markersize=10,
markerfacecolor='w', markeredgewidth=1.5, markeredgecolor='black')
plt.savefig(
'main.png',
format='png',
bbox_inches='tight'
)
plt.clf()
And this is the output:
And this is what I want (hacked with GIMP), notice how the negative tick labels are on a different side of the axes now.
I tried adding:
for tick in ax.xaxis.get_majorticklabels():
tick.set_verticalalignment("bottom")
as shown in answers to: How to move a tick's label in matplotlib? but that does not move the tick labels up enough, and makes the labels show on top of the axes instead.
Tested on matplotlib 3.2.2.

Answer 1

The following code will adjust the vertical alignment of the ticks depending one whether they are at a negative or positive x-value. However that's not enough because the labels are actually anchored at the bottom of the tick line. I'm therefore adjusting their y-position a little bit, but you have to play with the value to get the desired output
# adjust the xticks so that they are on top when x<0 and on the bottom when x≥0
ax.spines['top'].set_visible(True)
ax.spines['top'].set_position('zero')
ax.spines['bottom'].set_visible(True)
ax.spines['bottom'].set_position('zero')
ax.xaxis.set_tick_params(which='both', top=True, labeltop=True,
bottom=True, labelbottom=True)
fig.canvas.draw()
for tick in ax.xaxis.get_major_ticks():
print(tick.get_loc())
if tick.get_loc()<0:
tick.tick1line.set_visible(False)
tick.label1.set_visible(False)
else:
tick.tick2line.set_visible(False)
tick.label2.set_visible(False)
full code:
import math
import numpy as np
import matplotlib
import matplotlib.pyplot as plt
"""
Setup for a typical explanatory-style illustration style graph.
"""
h = 10
x = np.linspace(-np.pi, np.pi, 100)
y = h * np.sin(x)
rc = {
# Tick in the middle of the axis line.
'xtick.direction' : 'inout',
'ytick.direction' : 'inout',
# Bold is easier to read when we have few ticks.
'font.weight': 'bold',
'xtick.labelbottom': False,
'xtick.labeltop': True,
}
with plt.rc_context(rc):
fig, ax = plt.subplots()
ax.plot(x, y)
ax.set_title(
'2 sin(x), not $\\sqrt{2\\pi}$',
# TODO make LaTeX part bold?
# https://stackoverflow.com/questions/14324477/bold-font-weight-for-latex-axes-label-in-matplotlib
fontweight='bold',
# Too close otherwise.
# https://stackoverflow.com/questions/16419670/increase-distance-between-title-and-plot-in-matplolib/56738085
pad=20
)
# Custom visible plot area.
# ax.set_xlim(-3, 3)
ax.set_ylim(-2.5, 2.5)
# Axes
# Axes on center:
# https://stackoverflow.com/questions/31556446/how-to-draw-axis-in-the-middle-of-the-figure
ax.spines['left'].set_position('zero')
ax.spines['right'].set_visible(False)
ax.spines['bottom'].set_position('zero')
ax.spines['top'].set_visible(False)
# Axes with arrow:
# https://stackoverflow.com/questions/33737736/matplotlib-axis-arrow-tip
ax.plot(1, 0, ls="", marker=">", ms=10, color="k",
transform=ax.get_yaxis_transform(), clip_on=False)
ax.plot(0, 1, ls="", marker="^", ms=10, color="k",
transform=ax.get_xaxis_transform(), clip_on=False)
# Ticks
ax.xaxis.set_ticks_position('bottom')
ax.yaxis.set_ticks_position('left')
# Make ticks a bit longer.
ax.tick_params(width=1, length=10)
# Select tick positions
# https://stackoverflow.com/questions/12608788/changing-the-tick-frequency-on-x-or-y-axis-in-matplotlib
xticks = np.arange(math.ceil(min(x)), math.floor(max(x)) + 1, 1)
yticks = np.arange(math.ceil(min(y)) - 1, math.floor(max(y)) + 2, 1)
# Remove 0.
xticks = np.setdiff1d(xticks, [0])
yticks = np.setdiff1d(yticks, [0])
ax.xaxis.set_ticks(xticks)
ax.yaxis.set_ticks(yticks)
# Another approach. But because I want to be able to remove the 0,
# anyways, I just explicitly give all ticks instead.
# ax.xaxis.set_major_locator(matplotlib.ticker.MultipleLocator(1.0))
# ax.yaxis.set_major_locator(matplotlib.ticker.MultipleLocator(1.0))
for g,t in zip(ax.get_xticks(),ax.get_xticklabels()):
if g<0:
t.set_va('bottom')
else:
t.set_va('top')
t.set_transform(ax.transData)
t.set_position((g,0.15*-(g/abs(g))))
# Annotations.
ax.plot([0, np.pi/2], [h, h], '--r')
ax.plot([np.pi/2, np.pi/2], [h, 0], '--r')
ax.plot(np.pi/2, h, marker='o', linewidth=2, markersize=10,
markerfacecolor='w', markeredgewidth=1.5, markeredgecolor='black')
# adjust the xticks so that they are on top when x<0 and on the bottom when x≥0
ax.spines['top'].set_visible(True)
ax.spines['top'].set_position('zero')
ax.spines['bottom'].set_visible(True)
ax.spines['bottom'].set_position('zero')
ax.xaxis.set_tick_params(which='both', top=True, labeltop=True,
bottom=True, labelbottom=True)
fig.canvas.draw()
for tick in ax.xaxis.get_major_ticks():
print(tick.get_loc())
if tick.get_loc()<0:
tick.tick1line.set_visible(False)
tick.label1.set_visible(False)
else:
tick.tick2line.set_visible(False)
tick.label2.set_visible(False)