python pandas dataframe replace column values with null code example

Example 1: replace value of dataframe with another column

df['col1'] = np.where(df['col1'] == 0, df['col2'], df['col1'])
df['col1'] = np.where(df['col1'] == 0, df['col3'], df['col1'])

Example 2: fillna string

# importing pandas module 
import pandas as pd 
  
# making data frame from csv file 
nba = pd.read_csv("nba.csv") 
  
# replacing na values in college with No college 
nba["College"].fillna( method ='ffill', inplace = True)