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Adding new column to existing DataFrame in Pandas
Let’s discuss how to add new columns to the existing DataFrame in Pandas. There are multiple ways we can do this task.
Method #1: By declaring a new list as a column.
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Python3
# Import pandas packageimport pandas as pd# Define a dictionary containing Students datadata = {'Name': ['Jai', 'Princi', 'Gaurav', 'Anuj'], 'Height': [5.1, 6.2, 5.1, 5.2], 'Qualification': ['Msc', 'MA', 'Msc', 'Msc']}# Convert the dictionary into DataFramedf = pd.DataFrame(data)# Declare a list that is to be converted into a columnaddress = ['Delhi', 'Bangalore', 'Chennai', 'Patna']# Using 'Address' as the column name# and equating it to the listdf['Address'] = address# Observe the resultdf |
Output:
Note that the length of your list should match the length of the index column otherwise it will show an error.
Method #2: By using DataFrame.insert()
It gives the freedom to add a column at any position we like and not just at the end. It also provides different options for inserting the column values.
Python3
# Import pandas packageimport pandas as pd# Define a dictionary containing Students datadata = {'Name': ['Jai', 'Princi', 'Gaurav', 'Anuj'], 'Height': [5.1, 6.2, 5.1, 5.2], 'Qualification': ['Msc', 'MA', 'Msc', 'Msc']}# Convert the dictionary into DataFramedf = pd.DataFrame(data)# Using DataFrame.insert() to add a columndf.insert(2, "Age", [21, 23, 24, 21], True)# Observe the resultdf |
Output:
Method #3: Using Dataframe.assign() method
This method will create a new dataframe with a new column added to the old dataframe.
Python3
# Import pandas packageimport pandas as pd # Define a dictionary containing Students datadata = {'Name': ['Jai', 'Princi', 'Gaurav', 'Anuj'], 'Height': [5.1, 6.2, 5.1, 5.2], 'Qualification': ['Msc', 'MA', 'Msc', 'Msc']} # Convert the dictionary into DataFramedf = pd.DataFrame(data)# Using 'Address' as the column name and equating it to the listdf2 = df.assign(address = ['Delhi', 'Bangalore', 'Chennai', 'Patna']) # Observe the resultdf2 |
Output:
Method #4: By using a dictionary
We can use a Python dictionary to add a new column in pandas DataFrame. Use an existing column as the key values and their respective values will be the values for a new column.
Python3
# Import pandas packageimport pandas as pd# Define a dictionary containing Students datadata = {'Name': ['Jai', 'Princi', 'Gaurav', 'Anuj'], 'Height': [5.1, 6.2, 5.1, 5.2], 'Qualification': ['Msc', 'MA', 'Msc', 'Msc']}# Define a dictionary with key values of# an existing column and their respective# value pairs as the # values for our new column.address = {'Delhi': 'Jai', 'Bangalore': 'Princi', 'Patna': 'Gaurav', 'Chennai': 'Anuj'}# Convert the dictionary into DataFramedf = pd.DataFrame(data)# Provide 'Address' as the column namedf['Address'] = address# Observe the outputdf |
Output:
