CODEWITHSUNDEEP
pythonmatplotlib
not link
not link

Reputation: 870

pyplot twinx() tickmark overlap

Pardon my poor python skills, I am rather new to the language!

None the less, I am confused by the results I am getting from twinx() currently. I am not sure why when I twin the x axis, the ticks on the right hand side y axis seem to double.

import matplotlib.pyplot as plt

x = linspace(0,2*pi,100)
y = sin(x) + 100*rand(len(x))
z = cos(x) + 100*rand(len(x))
data = []
data.append(y)
data.append(z)

fig = plt.figure(1)
for kk in range(len(data)):
    ax1 = fig.add_subplot(111)
    ax1.plot(x.T, data[kk], 'b.-')

plt.show()

The first plot displays (to my mind) the correct behavior left Y axis

fig2 = plt.figure(2)
for kk in range(len(data)):
    ax3 = fig2.add_subplot(111)
    ax4 = ax3.twinx()
    ax4.plot(x.T, data[kk], 'b.-')

plt.show()

While the second plot (where all I have done is flip the axis) seems to have poor y tick behavior wherein the two 'curves' each get their own tick marks. right y axis

Any thoughts as to why this might be occurring would be greatly appreciated!

Upvotes: 3

Views: 5793

Answers (2)

Tanaya
Tanaya

Reputation: 21

If you take the call to twinx() and add_subplot() out of the loop, I think you'll get the figure you're after. Like so:

fig2 = plt.figure(2)
ax3 = fig2.add_subplot(111)
ax4 = ax3.twinx()
for kk in range(len(data)):
    ax4.plot(x.T, data[kk], 'b.-')

plt.show()

By the end of your loop you're calling twinx() twice, so you naturally get two twinned axes. Since they have different scales, the numbers overlap in an awkward way.

Upvotes: 2

Joe Kington
Joe Kington

Reputation: 284562

Because that's what twinx is supposed to do :)

Seriously, though, the point of twinx is to create an independent y-axis on the same plot. By default, it shows the ticks for the second, independent y-axis on the right hand side of the plot.

The idea is that you can do something like this using twinx (or twiny if you want two independent x-axes):

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()
ax2 = ax.twinx()

x = np.linspace(0, 10, 100)

ax.plot(x, np.sin(x), color='blue')
ax.set_ylabel(ylabel='Y-Value 1', color='blue')
ax.set_xlabel('Same X-values')

ax2.plot(x, x**3, color='green')
ax2.set_ylabel('Y-Value 2', color='green')

plt.show()

enter image description here

If you just want two curves that share the same axes, just plot them on the same axes. E.g.:

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()

x = np.linspace(0, 10, 100)
ax.plot(x, x, label='$y=x$')
ax.plot(x, 3 * x, label='$y=3x$')
ax.legend(loc='upper left')

ax.set(xlabel='Same X-values', ylabel='Same Y-values')

plt.show()

enter image description here

Upvotes: 2

Related Questions