Interactive bar plot using matplotlib with annotation change

Question

I'm trying to create a horizontal bar plot that can dynamically change with a slider. I've followed the recipe on the matplotib website and it works well for line data. The code:

def interactive_pyramid(ages_matrix, year_labels):
    fig, axs = plt.subplots()
    plt.subplots_adjust(bottom=0.25)
    l, = axs.plot(range(len(ages_matrix[0, :])), ages_matrix[0, :])
    axs.annotate(year_labels[0], xy=(0.85, 0.85), xycoords="axes fraction")
    axs.set_ylim([0,800])

    pprint (dir(axs))
    axcolor = 'lightgoldenrodyellow'
    axyear = plt.axes([0.25, 0.1, 0.5, 0.1], axisbg=axcolor)
    syear = Slider(axyear, 'Year', 0, ages_matrix.shape[0] - 1, 0)

    def update(val):
        year = syear.val
        # axs.barh(range(len(ages_matrix[0, :])), ages_matrix[val, :])
        l.set_ydata(ages_matrix[val, :])
        # axs.annotate(year_labels[year], xy=(0.85, 0.85), xycoords="axes fraction")
        axs.Annotation.remove()
        fig.canvas.draw()
    syear.on_changed(update)

ages_matrix is a 2d ndarray and year_labels is a 1d ndarray

two main questions:

• the axs.barh() does not return an object with a set_ydata() method do I can't change the y data. if I just draw the data again on the axs object it doesn't erase the previous information, resulting in a clutter of charts.
• the same happens with annotations - it does not erase the previous one.

Is there any way to efficiently erase the ax and draw it again? maybe some way to refresh the canvas?

Answer 1

That's what I came up with:

# Init Chart
fig, axs = plt.subplots()
plt.subplots_adjust(bottom=0.25)
axs.set_xlim([0,ages_matrix.max()*1.05])
# Initial Pyramid
pyramid = axs.barh(np.arange(len(ages_matrix[0, :])) * 5,
                   ages_matrix[0, :],
                   height=4.5)
# Annotation
ann = axs.annotate(year_labels[0], xy=(0.85, 0.85), xycoords="axes fraction")
# Slider
axcolor = 'lightgoldenrodyellow'
axyear = plt.axes([0.25, 0.1, 0.5, 0.1], axisbg=axcolor)
syear = Slider(axyear, 'Year', 0, ages_matrix.shape[0] - 1, 0)

def update(val):
    t = syear.val
    year = np.trunc(year_labels[t])
    day = (year_labels[t] - year) * 365
    ages = ages_matrix[t, :]
    for i, p in enumerate(pyramid):
        p.set_width(ages[i])
    ann.set_text("Year: {}\nDay: {}".format(int(year), int(day)))
    fig.canvas.draw()