Python Pandas – Propagate non-null values backward

Use the “method” parameter of the fillna() method. For backward fill, use the value ‘bfill’ as shown below −

fillna(method='bfill')

Let’s say the following is our CSV file opened in Microsoft Excel with some NaN values −

At first, import the required library −

import pandas as pd

Load data from a CSV file into a Pandas DataFrame −

dataFrame = pd.read_csv("C:\Users\amit_\Desktop\SalesData.csv") 

Example

Following is the code −

import pandas as pd # Load data from a CSV file into a Pandas DataFrame dataFrame = pd.read_csv("C:\Users\amit_\Desktop\SalesData.csv") print("DataFrame...\n",dataFrame) # propagate non null values backward res = dataFrame.fillna(method='bfill') print("\nDataFrame after backward fill...\n",res)

Output

This will produce the following output −

DataFrame...        Car   Reg_Price   Units 0      BMW        2500   100.0 1    Lexus        3500     NaN 2     Audi        2500   120.0 3   Jaguar        2000     NaN 4  Mustang        2500   110.0 DataFrame after backward fill...        Car   Reg_Price   Units 0      BMW        2500   100.0 1    Lexus        3500   120.0 2     Audi        2500   120.0 3   Jaguar        2000   110.0 4  Mustang 2500 110.0