data['days_employed'] = data['days_employed'].apply(abs)
days_employed_med = data.groupby(['education','income_type'], as_index = False)['days_employed'].median()

for index, row in days_employed_med.iterrows():
    education = row['education']
    income = row['income_type']
    data.loc[(data['days_employed'].isnull()) & (data['education'] == education) & (data['income_type'] == income), 'days_employed'] = days_employed_med[(days_employed_med['education'] == education) & (days_employed_med['income_type'] == income)]['days_employed']