Matplotlib step plot rotation

Question

I'm trying to rotate correctly the matplotlib step plot. First I swapped the x and y axes and reversed the y axis. I made the step plot again. However, the direction of the step line (blue color) was not as desired in the right picture and the red colored stepping line is the superimposed rotated image of the left picture. Here is my code

import numpy as np
import matplotlib.pyplot as plt

x = np.arange(14)
y = np.sin(x / 2)

fig, (ax, bx) = plt.subplots(nrows=1, ncols=2, figsize=(11.5, 5.5))
fig.subplots_adjust(left=0.08, bottom=0.13, top=0.98, right=0.97, wspace=0.2, hspace=0.0)

ax.step(x, y, where='mid', c='r')
ax.plot(x, y, 'o--', color='grey', alpha=0.3)

bx.invert_yaxis()
bx.step(y, x, where='pre', c='b')
bx.plot(y, x, 'o--', color='grey', alpha=0.3)

plt.show()

I am trying to make red colored step plot as shown in the right picture. How can I do this?

user_13410397 · Answer

The desired step-style can be obtained by shifting a little bit the second coordinates and using where=pre.

def plot_step_invert_mid(x, y, *args, **kwargs):
    y_new = np.insert(y, 0, y[0])
    y_new = 0.5 * (y_new[1:] + y_new[:-1])
    x_new = np.append(x, x[-1])
    y_new = np.append(y_new, y[-1])
    plt.step(x_new, y_new, where="pre", *args, **kwargs)

fig, (ax, bx) = plt.subplots(nrows=1, ncols=2, figsize=(11.5, 5.5))
fig.subplots_adjust(left=0.08, bottom=0.13, top=0.98, right=0.97, wspace=0.2, hspace=0.0)

ax.step(x, y, where="mid", c='r')
ax.plot(x, y, 'o--', color='grey', alpha=0.3)

bx.invert_yaxis()
plot_step_invert_mid(y, x)
bx.plot(y, x, 'o--', color='grey', alpha=0.3)

user_9214357 · Answer

I suggest you to interpolate your original curve with scipy.interpolate.interp1d rather then use the matplotlib.pyplot.step method of plotting. This because interp1d generates a new vector that you can manipulate as you wish.
In the code below:

x and y are the original curve vectors (length 14)
xx and yy are the original curve interpolated vectors (length N)

In order to rotate the plot you can simply swap x with y and xx with yy in plt.plot:

import numpy as np
import matplotlib.pyplot as plt
from scipy.interpolate import interp1d

x = np.arange(14)
y = np.sin(x/2)

N = 1000
xx = np.linspace(0, 13, N)
yy = interp1d(x, y, kind = 'nearest')(xx)

fig, (ax, bx) = plt.subplots(nrows = 1, ncols = 2, figsize = (11.5, 5.5))
fig.subplots_adjust(left = 0.08, bottom = 0.13, top = 0.98, right = 0.97, wspace = 0.2, hspace = 0.0)

ax.plot(xx, yy, 'r')
ax.plot(x, y, 'o--', color = 'grey', alpha = 0.3)

bx.invert_yaxis()
bx.plot(yy, xx, 'r')
bx.plot(y, x, 'o--', color = 'grey', alpha = 0.3)

plt.show()

Matplotlib step plot rotation

2 Answers