IPython Notebook widgets for Matplotlib interactivity

Question

I would like to use the ipython notebook widgets to add some degree of interactivity to inline matplotlib plots.

In general the plot can be quite heavy and I want to on

Answer 1

I have a hacky workaround that will only display one figure. The problem seems to be that there are two points in the code that generate a figure and really, we only want the second one, but we can't get away with inhibiting the first. The workaround is to use the first one for the first execution and the second one for all subsequent ones. Here's some code that works by switching between the two depending on the initialized flag:

%matplotlib inline
import matplotlib.pyplot as plt
from IPython.html.widgets import interact, interactive, fixed
from IPython.html import widgets
from IPython.display import clear_output, display, HTML

class InteractiveCursor(object):
    initialized = False
    fig = None
    ax = None
    vline = None
    hline = None

    def initialize(self):
        self.fig, self.ax = plt.subplots()
        self.ax.plot([3,1,2,4,0,5,3,2,0,2,4])
        self.vline = self.ax.axvline(1)
        self.hline = self.ax.axhline(0.5)

    def set_cursor(self, x, y):
        if not self.initialized:
            self.initialize()

        self.vline.set_xdata((x, x))
        self.hline.set_ydata((y, y))

        if self.initialized:
            display(self.fig)
        self.initialized = True

ic = InteractiveCursor()
def set_cursor(x, y):
    ic.set_cursor(x, y)

interact(set_cursor, x=(1, 9, 0.01), y=(0, 5, 0.01));

My opinion is that this should be considered a bug. I tried it with the object oriented interface and it has the same problem.

Answer 2

You can do this in a very strait forward way using the new(ish) notebook backend

%matplotlib notebook
import matplotlib.pyplot as plt
from IPython.html.widgets import interactive

fig, ax = plt.subplots()
ax.plot(range(5))


vline = ax.axvline(1, color='k')
hline = ax.axhline(0.5, color='k')

def set_cursor(x, y):
    vline.set_xdata((x, x))
    hline.set_ydata((y, y))
    ax.figure.canvas.draw_idle()

and in a separate cell:

interactive(set_cursor, x=ax.get_xlim(), y=ax.get_ylim())

This will still re-draw the entire figure every time you move the cursor because notebook does not currently support blitting (which is being worked on https://github.com/matplotlib/matplotlib/pull/4290 )

Answer 3

The solution turns out to be really simple. To avoid showing the first figure we just need to add a close() call before the interact call.

Recalling the example of the question, a cell like this will correctly show a single interactive figure (instead of two):

fig, ax = plt.subplots()
ax.plot([3,1,2,4,0,5,3,2,0,2,4])
plt.close(fig)

vline = ax.axvline(1)
hline = ax.axhline(0.5)

def set_cursor(x, y):
    vline.set_xdata((x, x))
    hline.set_ydata((y, y))
    display(fig)

interact(set_cursor, x=(1, 9, 0.01), y=(0, 5, 0.01))

A cleaner approach is defining the function add_cursor (in a separate cell or script):

def add_cursor(fig, ax):
    plt.close(fig)

    vline = ax.axvline(1, color='k')
    hline = ax.axhline(0.5, color='k')

    def set_cursor(x, y):
        vline.set_xdata((x, x))
        hline.set_ydata((y, y))
        display(fig)

    interact(set_cursor, x=ax.get_xlim(), y=ax.get_ylim())

and then call it whenever we want to add an interactive cursor:

fig, ax = plt.subplots()
ax.plot([3,1,2,4,0,5,3,2,0,2,4])
add_cursor(fig, ax)