How do i animate subplots in python using matplotlib

Question

import sqlite3
import matplotlib.animation as animation
import matplotlib.pyplot as plt

def animate(i):

    con = sqlite3.connect('newbase1.db')
    c = con.cursor()

    c.execute('SELECT Cell_1_V,Cell_2_V,Cell_1_T, time_stamp FROM Measurements')
    data = c.fetchall()

    Cell_1_V = []
    Cell_2_V = []
    Cell_1_T = []
    tim = []

    for row in data:
        Cell_1_V.append(row[0])
        Cell_2_V.append(row[1])
        Cell_1_T.append(row[2])
        tim.append(row[3])


    fig , (sb1,sb2) = plt.subplots(nrows=2,ncols= 1)
    sb1.set_xlabel("TIME---->")
    sb1.set_ylabel("VOLTAGE--->")
    sb2.set_xlabel("TIME---->")
    sb2.set_ylabel("TEMP--->")
    sb1.plot(tim,Cell_1_V,label='Cell_1_V')
    sb2.plot(tim, Cell_1_T, label='Cell_1_T')
    sb1.legend(loc='upper right')
    sb2.legend(loc='upper right')


ani = animation.FuncAnimation(plt.gcf(), animate, interval=500)
plt.tight_layout()
plt.show()

The above is the code where I am trying to animate both subplots in the same figure but all i get is an empty plot. Any help would be appreciated.

Thanks in advance.

Answer 1

The basics of animation are initialization and updating data within the animation function. This is the same for a single graph and a subplot. The data has been created appropriately; the x-axis is graphed as a date.

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation
import matplotlib.dates as mdates
from matplotlib.dates import DateFormatter

time_rng = pd.date_range('2021-01-01', freq='1d', periods=100)
vol1 = np.random.randn(100)*10
vol2 = np.random.randn(100)*10
temp1 = np.random.randn(100)+30

data = pd.DataFrame({'VOLTAGE1':vol1, 'VOLTAGE2':vol2, 'TEMP':temp1,'TIME':pd.to_datetime(time_rng)})

Cell_1_V, Cell_2_V, Cell_1_T, tim = [], [], [], []

for idx,row in data.iterrows():
    Cell_1_V.append(row[0])
    Cell_2_V.append(row[1])
    Cell_1_T.append(row[2])
    tim.append(row[3])

fig , (sb1,sb2) = plt.subplots(nrows=2,ncols= 1)

sb1.set(xlim=(mdates.date2num(tim[0]),mdates.date2num(tim[-1])), ylim=(data.VOLTAGE1.min(), data.VOLTAGE1.max()))
sb2.set(xlim=(mdates.date2num(tim[0]),mdates.date2num(tim[-1])), ylim=(data.TEMP.min(), data.TEMP.max()))
fig.subplots_adjust(hspace=0.4)

sb1.set_xlabel("TIME---->")
sb1.set_ylabel("VOLTAGE--->")
sb2.set_xlabel("TIME---->")
sb2.set_ylabel("TEMP--->")
line1, = sb1.plot([], [], label='Cell_1_V', color='C0')
line2, = sb2.plot([], [], label='Cell_1_T', color='C1')
sb1.legend(loc='upper right')
sb2.legend(loc='upper right')
date_fmt = DateFormatter("%Y-%m-%d")
sb1.xaxis.set_major_formatter(date_fmt)
sb2.xaxis.set_major_formatter(date_fmt)
line = [line1, line2]

def animate(i):
    line[0].set_data(mdates.date2num(tim[:i]), Cell_1_V[:i])
    line[1].set_data(mdates.date2num(tim[:i]), Cell_1_T[:i])
    return line
    
ani = FuncAnimation(fig, animate, frames=len(data), interval=200, repeat=False)
# plt.tight_layout()
plt.show()