import pandas as pd
import numpy as np
raw_data = {'name': ['Willard Morris', 'Al Jennings', 'Omar Mullins', 'Spencer McDaniel'],
'age': [20, 19, 22, 21],
'favorite_color': ['blue', 'red', 'yellow', "green"],
'grade': [88, 92, 95, 70]}
df = pd.DataFrame(raw_data, index = ['Willard Morris', 'Al Jennings', 'Omar Mullins', 'Spencer McDaniel'])
df
#First, we have to create the NaN values
df = df.replace(20,np.NaN)
df = df.replace(70,np.NaN)
df
#Now, we can replace them
df = df.fillna(0)
df