Add a column to DataFrame Columns

We can add a new column to an existing DataFrame using different ways. For the demonstration, first, we have to write a code to read the existing file, which consists of some columns in a DataFrame.

The above code read the existing csv file and shows the data values column as the output.

Output

	
Name
	
Hire Date
	
Salary
	
Leaves Remaining


	
0 John Idle
	
03/15/14
	
50000.0
	
10


	
1 Smith Gilliam
	
06/01/15
	
65000.0
	
8


	
2 Parker Chapman
	
05/12/14
	
45000.0
	
10


	
3 Jones Palin
	
11/01/13
	
70000.0
	
3


	
4 Terry Gilliam
	
08/12/14
	
48000.0
	
7


	
5 Michael Palin
	
05/23/13
	
66000.0
	
8

Add new columns to a DataFrame using [] operator

If we want to add any new column at the end of the table, we have to use the [] operator. Let's add a new column named "Age" into "aa" csv file.

This code adds a column "Age" at the end of the aa csv file. So, the new table after adding a column will look like this:

    Name           Hire Date    Salary    Leaves Remaining  Age
0  John Idle        03/15/14    50000.0     10              24
1  Smith Gilliam    06/01/15    65000.0     8               24 
2  Parker Chapman   05/12/14    45000.0     10              24
3  Jones Palin      11/01/13    70000.0     3               24
4  Terry Gilliam    08/12/14    48000.0     7               24
5  Michael Palin    05/23/13    66000.0     8               24

In the above code, Age value has defined the universal value that means its value is common to all the rows. If we specify a column name that does not exist, Pandas will throw an error.

For ex:

In the above code, Pandas will throw an error because the Designation column does not exist.

But if we assign a value to that column, Pandas will generate a new column automatically at the end of the table.

Add new columns in a DataFrame using insert()

We can also add a new column at any position in an existing DataFrame using a method name insert.

For the demonstration, first, we have to write a code to read the existing file that consists of some columns in a DataFrame.

The above code read the existing csv file and shown the data values column in the output.

Output

    Name           Hire Date   Salary    Leaves Remaining
0  John Idle       03/15/14    50000.0    10
1  Smith Gilliam   06/01/15    65000.0    8
2  Parker Chapman  05/12/14    45000.0    10
3  Jones Palin     11/01/13    70000.0    3
4  Terry Gilliam   08/12/14    48000.0    7
5  Michael Palin   05/23/13    66000.0    8

Let's add a new column name "Department" into an existing "aa" csv file using insert method.

Output

   Name            Hire Date   Department   Salary    Leaves Remaining
0  John Idle       03/15/14     B.Sc        50000.0    10
1  Smith Gilliam   06/01/15     B.Sc        65000.0    8
2  Parker Chapman  05/12/14     B.Sc        45000.0    10
3  Jones Palin     11/01/13     B.Sc        70000.0    3
4  Terry Gilliam   08/12/14     B.Sc        48000.0    7
5  Michael Palin   05/23/13     B.Sc        66000.0    8