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How to update a plot on same figure during the loop?
  • Last Updated : 24 Feb, 2021

We can use matplotlib to update a plot on every iteration during the loop. With the help of matplotlib.pyplot.draw() function we can update the plot on the same figure during the loop.

Using matplotlib.pyplot.draw(): It is used to update a figure that has been changed. It will redraw the current figure.

Syntax: figure.canvas.draw()

Before this we use figure.ion() function to run a GUI event loop. Without using figure.ion() we may not be able to see the GUI plot.


In the given example firstly we are importing all the necessary libraries that we are going to use. And then creating X and Y. X holds the values from 0 to 10 which evenly spaced into 100 values. e.g. we are creating values from 2 to 3 with evenly spaced 5 values (np.linspace(2, 3, 5)) It should output like these 5 values from 2 to 3 evenly spaced array([2 , 2.25, 2.5 , 2.75, 3 ]). After that we are initializing GUI using plt.ion() function, now we have to create a subplot, so we can plot X and Y values. After that we are running a for loop up to some iterations and creating a new_y values which hold our updating value then we are updating the values of X  and Y using set_xdata() and set_ydata(). And canvas.draw() will plot the updated values and canvas.flush_events() holds the GUI event till the UI events have been processed. This will run till the loop ends and values will be updated continuously.



# importing libraries
import numpy as np
import time
import matplotlib.pyplot as plt
# creating initial data values
# of x and y
x = np.linspace(0, 10, 100)
y = np.sin(x)
# to run GUI event loop
# here we are creating sub plots
figure, ax = plt.subplots(figsize=(10, 8))
line1, = ax.plot(x, y)
# setting title
plt.title("Geeks For Geeks", fontsize=20)
# setting x-axis label and y-axis label
# Loop
for _ in range(50):
    # creating new Y values
    new_y = np.sin(x-0.5*_)
    # updating data values
    # drawing updated values
    # This will run the GUI event
    # loop until all UI events
    # currently waiting have been processed


Updating plot

Here, figure.canvas.flush_events()  is used to clear the old figure before plotting the updated figure.

Example 2: In this example code, we are updating the value of y in a loop using set_xdata() and redrawing the figure every time using canvas.draw().


from math import pi
import matplotlib.pyplot as plt
import numpy as np
import time
# genrating random data values
x = np.linspace(1, 1000, 5000)
y = np.random.randint(1, 1000, 5000)
# enable interactive mode
# creating subplot and figure
fig = plt.figure()
ax = fig.add_subplot(111)
line1, = ax.plot(x, y)
# setting labels
plt.title("Updating plot...")
# looping
for _ in range(50):
    # updating the value of x and y
    # re-drawing the figure
    # to flush the GUI events


Updating plot.

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