#Loading Libraries 
import pandas as pd
import numpy as np
from sklearn.impute import SimpleImputer

#Creating dataset
data = pd.DataFrame({'SocialApps':['facebook', 'whatsapp', 
      'instagram', 'facebook', np.nan]})

# Creating a SimpleImputer object
imp = SimpleImputer(strategy='most_frequent')

"""" Impute the missing values in the 'SocialApps' 
    column of the 'data' DataFrame"""

# Fitting transform
data['SocialApps'] = imp.fit_transform(data[['SocialApps']])

#Printing result
print(data['SocialApps'])