python - Jupyter Notebook: interactive plot with widgets

Question

I am trying to generate an interactive plot that depends on widgets. The problem I have is that when I change parameters using the slider, a new plot is done after the previous one, instead I would expect only one plot changing according to the parameters.

Example:

from ipywidgets import interact, interactive, fixed, interact_manual
import ipywidgets as widgets

import matplotlib.pyplot as plt
%matplotlib inline

import numpy as np

def plot_func(freq):
    x = np.linspace(0, 2*np.pi)
    y = np.sin(x * freq)
    plt.plot(x, y)

interact(plot_func, freq = widgets.FloatSlider(value=7.5,
                                               min=1,
                                               max=5.0,
                                               step=0.5))

After moving the slider to 4.0, I have:

while I just want one figure to change as I move the slider. How can I achieve this?

(I am using Python 2.7, matplotlib 2.0 and I have just updated notebook and jupyter to the latest version. let me know if further info is needed.)

Answer 1

As you want to change the figure, instead of creating a new one, may I suggest the following way:

1. Use an interactive backend; %matplotlib notebook
2. Update the line in the plot, instead of drawing new ones.

So the code could look something like this:

%matplotlib notebook
from ipywidgets import *
import numpy as np
import matplotlib.pyplot as plt

x = np.linspace(0, 2 * np.pi)
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
line, = ax.plot(x, np.sin(x))

def update(w = 1.0):
    line.set_ydata(np.sin(w * x))
    fig.canvas.draw_idle()

interact(update);

Alternatively you may use plt.show() as in this answer.