How do I use a function as the 'frames' parameter in matplotlib animation?

Question

I am trying create a sorting visualizer like this https://www.youtube.com/watch?v=SMiXoz2p6Ww . I want to use my bubbleSort function as the 'frames' parameter in matplotlib's animation. Documentation says the function needs to be called at each frame but mine runs all at once. How do I break it down into steps so that each step can be shown as a frame?

from random import randint
import matplotlib.pyplot as plt
import matplotlib.animation as animation

#Bubble sort to put array in order
def bubbleSort(array):
    swapped = True
    for i in range(len(array)-1):
        if not swapped:
            break

        swapped = False

        for j in range(0, size-1-i):
            if array[j] > array[j+1]:
                array[j], array[j+1] = array[j+1], array[j]
                swapped = True

            yield array

if __name__ == "__main__":
    #Create array
    size = int(input("Pick an integer from 50 to 100: "))

    while size < 50 or size > 100:
        size = int(input("Please enter a valid input: "))

    A = []

    for i in range(size):
        value = randint(1,100)
        A.append(value)
    print(A)

    method = bubbleSort(A)

    #Create graph for sort visualizer
    fig, ax = plt.subplots()
    ax.set_title("Bubble Sort")

    ax.set_xlim(0, size)
    ax.set_ylim(0, 100)

    bars = ax.bar(range(len(A)), A, align="edge")
    zipped = zip(bars, A)

    text = ax.text(0.02, 0.95, "", transform=ax.transAxes)

    #Function to update graph
    count = [0]
    def update(A, bars, count):
        for bar,val in zipped:
            bar.set_height(val)
        count[0] += 1
        text.set_text("Number of operations: " + str(count))

    #Animation for graph
    ani = animation.FuncAnimation(fig, func=update, fargs=(bars, count), frames=method, interval=1, repeat=False)

    #Show graph
    plt.show()

I've tried using return and yield in the bubbleSort function but haven't been able to get it to work yet.

shu · Accepted Answer · 2020-02-20 22:52:53Z

1

In your 'update' function you set the height of the bars to be val, (which is set to be A = the array itself) This is why you constantly see the same bars.

You need to use the generator which return from the function using 'next(Method)' to get each step in the algorithm.

You can change the 'update' function to this code:

def update(A, bars, count):
    currentList = next(method)
    for i in range(len(bars)):
        bars[i].set_height(currentList[i])
    count[0] += 1
    text.set_text("Number of operations: " + str(count))

answered Feb 20, 2020 at 22:52

shu

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