Adding a new column to existing DataFrame in Pandas in Python


In this tutorial, we are going to learn how to add a new column to the existing DataFrame in pandas. We can have different methods to add a new column. Let's all of them.

Using List

We can add a new column using the list. Follow the steps to add a new column.

Algorithm

1. Create DataFrame using a dictionary.
2. Create a list containing new column data. Make sure that the length of the list matches the length of the data which is already present in the data frame.
3. Add the list to the DataFrame like dictionary element.

Let's see one example.

Example

# importing pandas
import pandas as pd
# creating a DataFrame
data = {
   'Name': ['Hafeez', 'Aslan', 'Kareem'],
   'Age': [19, 18, 15],
   'Profession': ['Pythoneer', 'Programmer', 'Student']
}
dataframe = pd.DataFrame(data)
print('-----------Before adding a new column----------')
print(dataframe)
print('\n\n')
# creating a list for new column
places = ['Nellore', 'Mumbai', 'Andhra']
# we are using 'Places' as column name
# adding the list to the dataframe as column
dataframe['Places'] = places
print('---------------After adding a new column------------')
print(dataframe)

Output

If you run the above program you will get the following results.

-----------Before adding a new column----------
Name Age Profession
0 Hafeez 19 Pythoneer
1 Aslan 18 Programmer
2 Kareem 15 Student
---------------After adding a new column------------
Name Age Profession Places
0 Hafeez 19 Pythoneer Nellore
1 Aslan 18 Programmer Mumbai
2 Kareem 15 Student Andhra

DataFrame.insert()

There is a built-in method called insert() to add a new column. Steps to follow.

Algorithm

1. Create DataFrame using dictionary.
2. Create a list containing new column data. Make sure that the length of the list matches the length of the data which is already present in the data frame.
3. Insert the data into the DataFrame using DataFrame.insert(index, column_name, data)
method.

Example

# importing pandas
import pandas as pd
# creating a DataFrame
data = {
   'Name': ['Hafeez', 'Aslan', 'Kareem'],
   'Age': [19, 18, 15],
   'Profession': ['Pythoneer', 'Programmer', 'Student']
}
dataframe = pd.DataFrame(data)
print('-----------Before adding a new column----------')
print(dataframe)
print('\n\n')
# creating a list for new column
places = ['Nellore', 'Mumbai', 'Andhra']
# we are using 'Places' as column name
# adding the list to the dataframe as column using insert(index, column_name, data)
dataframe.insert(2, 'Places', data)
print('---------------After adding a new column------------')
print(dataframe)

Output

If you run the above program, you will get the following results.

-----------Before adding a new column----------
Name Age Profession
0 Hafeez 19 Pythoneer
1 Aslan 18 Programmer
2 Kareem 15 Student
---------------After adding a new column------------
Name Age Places Profession
0 Hafeez 19 Name Pythoneer
1 Aslan 18 Age Programmer
2 Kareem 15 Profession Student

DataFrame.assign()

This method takes one argument i.e.., a list of data and adds it to the data frame as a column at the end.

Algorithm

1. Create DataFrame using a dictionary.
2. Create a list containing new column data. Make sure that the length of the list matches the length of the data which is already present in the data frame.
3. Insert the data into the DataFrame using DataFrame.assign(column_name = data)
method. It returns a new data frame. So, we have to store it.
4. Print the new data frame.

Let's see an example.

Example

# importing pandas
import pandas as pd
# creating a DataFrame
data = {
   'Name': ['Hafeez', 'Aslan', 'Kareem'],
   'Age': [19, 18, 15],
   'Profession': ['Pythoneer', 'Programmer', 'Student']
}
dataframe = pd.DataFrame(data)
print('-----------Before adding a new column----------')
print(dataframe)
print('\n\n')
# creating a list for new column
places = ['Nellore', 'Mumbai', 'Andhra']
# we are using 'Places' as column name
# adding the list to the dataframe as column using assign(column_name = data)
new_dataframe = dataframe.assign(Places = places)
print('---------------After adding a new column------------')
print(new_dataframe)

Output

If you run the above program, you will get the following results.

-----------Before adding a new column----------
Name Age Profession
0 Hafeez 19 Pythoneer
1 Aslan 18 Programmer
2 Kareem 15 Student
---------------After adding a new column------------
Name Age Profession Places
0 Hafeez 19 Pythoneer Nellore
1 Aslan 18 Programmer Mumbai
2 Kareem 15 Student Andhra

Conclusion

If you have any doubts regarding the tutorial, mention them in the comment section.

raja
Published on 04-Nov-2019 07:26:34
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