Create a new column in Pandas DataFrame based on the existing columns

While working with data in Pandas, we perform a vast array of operations on the data to get the data in the desired form. One of these operations could be that we want to create new columns in the DataFrame based on the result of some operations on the existing columns in the DataFrame. Let’s discuss several ways in which we can do that.

Given a Dataframe containing data about an event, we would like to create a new column called ‘Discounted_Price’, which is calculated after applying a discount of 10% on the Ticket price.

Solution #1: We can use DataFrame.apply() function to achieve this task.

# importing pandas as pd
import pandas as pd

# Creating the DataFrame
df = pd.DataFrame({'Date':['10/2/2011', '11/2/2011', '12/2/2011', '13/2/2011'],
                    'Event':['Music', 'Poetry', 'Theatre', 'Comedy'],
                    'Cost':[10000, 5000, 15000, 2000]})

# Print the dataframe
print(df)

Output :

Now we will create a new column called ‘Discounted_Price’ after applying a 10% discount on the existing ‘Cost’ column.

# using apply function to create a new column
df['Discounted_Price'] = df.apply(lambda row: row.Cost -
                                  (row.Cost * 0.1), axis = 1)

# Print the DataFrame after addition
# of new column
print(df)

Output :

Solution #2: We can achieve the same result by directly performing the required operation on the desired column element-wise.

# importing pandas as pd
import pandas as pd

# Creating the DataFrame
df = pd.DataFrame({'Date':['10/2/2011', '11/2/2011', '12/2/2011', '13/2/2011'],
                    'Event':['Music', 'Poetry', 'Theatre', 'Comedy'],
                    'Cost':[10000, 5000, 15000, 2000]})

# Create a new column 'Discounted_Price' after applying
# 10% discount on the existing 'Cost' column.

# create a new column
df['Discounted_Price'] = df['Cost'] - (0.1 * df['Cost'])

# Print the DataFrame after
# addition of new column
print(df)

Output :