change color of new points using animate of matplotlib

Question

I am trying to do an animated plot of a simple sine function where each new point is colored in red and old (meaning: already plotted) dots in gray. I am trying to follow this post since it does what I want with curves. Can someone please tell me what is wrong with my piece of code ?

Here it is:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation


x1 = np.linspace(0,10,1000)
y1 = np.sin(2*np.pi*x1)

fig, ax = plt.subplots()

def init():
    ax.set_xlim([0, 5])
    ax.set_ylim([-2, 2])
    return graph,


graph = None

def animate(i):
    global graph

    if graph is not None:
        graph.set_color('gray')
    graph, = ax.plot(x1[:i+1], y1[:i+1], '*r')
    return graph

ani = animation.FuncAnimation(fig, animate, init_func=init, frames=20, interval=20)

plt.show()

Thank you

Answer 1

I have written a more proper code.

# Import modules
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
# ------------------------------------------ #

# Define the data points
x = np.linspace(0.0, 2.0*np.pi, 80, endpoint=True)
y = np.sin(x)

# Define the figure and axes of plot
fig, ax = plt.subplots(figsize=(16,16))

# Define a list that stores temporary data points
# [[x values], [y values]]
data_points = [[], []]

# Define the index of the last data point that needs to be plotted
# For example, if index = 5, data_points[0][-1] = x[5] and data_points[1][-1] = y[5]
index = 0

# Animation loop
def animate(i):
     # Global variables
     global data_points, index

     # Clear the plot
     ax.clear()

     # Append a data point to the list
     data_points[0].append(x[index])
     data_points[1].append(y[index])

     # Update the index
     index += 1

     # Reset the index and points 
     # if index is out of range
     if (index == len(x)):
          index = 0
          data_points = [[], []]
          
     # Scatter the points
     plt.scatter(x=data_points[0], y=data_points[1], color="grey")
     plt.scatter(x=data_points[0][-1], y=data_points[1][-1], color="red") # Last point is red

     # Set the xy limits
     ax.set_xlim(min(x), max(x))
     ax.set_ylim(min(y), max(y))


# Calling the animation function
ani = FuncAnimation(fig, animate, interval=20)

plt.show()

This yields:

I hope this helps !