Insert New Column Into a Dataframe in Python

Dataframes are often used to handle tabular data in python. In this article, we will discuss how we can insert a new column into a dataframe in python.

Insert New Column Into a Dataframe by Indexing in Python

To add a new column into a dataframe, we can use indexing in the same way we add a key-value pair in a python dictionary. In this approach, we will first put all the elements of the column that needs to be inserted into a list. After that, we will add the list as a new column into the dataframe using the following syntax.

datframe_name[column_name]= element_list

Here, 

• datframe_name is the name of the dataframe into which the column has to be inserted.
• column_name represents an string that contains the name of the new column.
• element_list  denotes list containing the elements that will be inserted to the dataframe.

Following is the python source code to insert a new column into a dataframe by indexing.

import pandas as pd

df = pd.read_csv('Demo.csv')
print("The dataframe before inserting the column:")
print(df)
column_data = [180, 164, 170]
df['Height'] = column_data
print("The dataframe after inserting the column:")
print(df)

Output:

The dataframe before inserting the column:
   Roll    Name Language
0     1  Aditya   Python
1     2     Sam     Java
2     3   Chris      C++
The dataframe after inserting the column:
   Roll    Name Language  Height
0     1  Aditya   Python     180
1     2     Sam     Java     164
2     3   Chris      C++     170

Insert New Column Into a Dataframe Using the assign() Method

Instead of using indexing, we can use the assign() method to add a new column into the dataframe. The assign() method, when invoked on a dataframe, takes the column name and the list of elements of the new column as a keyword argument using the following syntax.

datframe_name.assign(column_name= element_list)

Here,

• datframe_name is the name of the dataframe into which the column has to be inserted.
• column_name denotes the name of the new column.
• element_list  is the list containing the elements that will be inserted to the dataframe.

After execution, the assign() method inserts the column into the dataframe and returns the updated dataframe as shown below.

import pandas as pd

df = pd.read_csv('Demo.csv')
print("The dataframe before inserting the column:")
print(df)
column_data = [180, 164, 170]
df = df.assign(Height=column_data)
print("The dataframe after inserting the column:")
print(df)

Output:

The dataframe before inserting the column:
   Roll    Name Language
0     1  Aditya   Python
1     2     Sam     Java
2     3   Chris      C++
The dataframe after inserting the column:
   Roll    Name Language  Height
0     1  Aditya   Python     180
1     2     Sam     Java     164
2     3   Chris      C++     170

The above approaches are used to insert the new column at the end. We can also insert new columns at any position in the dataframe. For that, we can use the insert() method.

Insert New Column Into a Dataframe Using the insert() Method

With the insert() method, we can insert a new column at any position in the dataframe. The insert() method, when invoked on a dataframe, takes the position at which the new column will be inserted as its first input argument, the name of the new column as the second input argument, the list containing the elements of the new column as the third input argument. After execution, it inserts the column at the specified position in the dataframe. You can observe this in the following example.

import pandas as pd

df = pd.read_csv('Demo.csv')
print("The dataframe before inserting the column:")
print(df)
column_data = [180, 164, 170]
df.insert(1, 'Height', column_data)
print("The dataframe after inserting the column:")
print(df)

Output:

The dataframe before inserting the column:
   Roll    Name Language
0     1  Aditya   Python
1     2     Sam     Java
2     3   Chris      C++
The dataframe after inserting the column:
   Roll  Height    Name Language
0     1     180  Aditya   Python
1     2     164     Sam     Java
2     3     170   Chris      C++

Conclusion

In this article, we have discussed three approaches to insert a new column into a dataframe in python. To know more about python programming, you can read this article on list comprehension in python. You might also like this article on dictionary comprehension in python.