Using a slider to display portions of barplot on a tkinter canvas: How to remove the initial entire barplot?

Question

I have a barplot with 20 labels and corresponding values, which is embedded on a tkinter figure canvas. A slider enables the user to view 5 bar values at a time. Adapting the approach at Python: Embed a matplotlib plot with slider in tkinter properly I have the following:

import random
import numpy as np
import matplotlib
import tkinter as Tk
import matplotlib.pyplot as plt
from matplotlib.widgets import Slider
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg

matplotlib.use('TkAgg')

root = Tk.Tk()
root.wm_title("Barplot with slider")

fig = plt.Figure()
canvas = FigureCanvasTkAgg(fig, root)
canvas.draw()
canvas.get_tk_widget().pack(side=Tk.TOP, fill=Tk.BOTH, expand=1)

channels=
['a','b','c','d','e','f','g','h','i','j','k','m','n','o','p','q','r','s','t','u']

X=range(len(channels))
Y=np.random.randint(0,100, len(X))
M=max(Y)

N=5

ax=fig.add_subplot(111)
ax.axis([0, N, 0,M])

ax.set_xticks(range(len(channels)))
ax.set_xticklabels(channels)
fig.subplots_adjust(bottom=0.25)

ax.bar(X,Y,width=0.7,align='center',color='green',ecolor='black')

ax_time = fig.add_axes([0.12, 0.1, 0.78, 0.03])
s_time = Slider(ax_time, 'Channels', 0, len(X)-N, valinit=0,valstep=1)


def update(val):
    N=5
    pos = s_time.val
    ax.axis([pos-1/2, pos+N-1/2, 0,M+1])
    fig.canvas.draw_idle()

s_time.on_changed(update)

Tk.mainloop()

It works fine, but there's one little thing I find annoying. When one runs the module, the first thing to appear is a barplot showing all 20 bars. I don't want that, as it is aesthetically unpleasing if I have a large number of bars.

Instead, I want the very first plot to appear on my canvas consist of only the first 5 bars labelled, 'a','b','c','d','e'.

Answer 1

Since you already have your update function setup, simply set the default value to 0:

...

s_time.on_changed(update)
s_time.set_val(0)

root.mainloop()