Pandas Data Frame Insert Method

The data frame insert method is used to add a new column at the specified position in a data frame.
If a newly added column name already exists then an error occurs.

Syntax of insert method

An example of the insert to add a new column

For our examples, we have the following data frame created by using this Python program:

Code:

import pandas as pd

inflation_data = {

  "Year": [2015, 2016, 2016, 2017],

  "Inflation": ['1.75%', '2%', '3%', '3.5%']

}


#Creating a Data frame with two columns

df_inf = pd.DataFrame(inflation_data)


#Display Data Frame

print(df_inf)

Data Frame:

   Year Inflation

0  2015     1.75%

1  2016        2%

2  2016        3%

3  2017      3.5%

In the example below, we will only use three arguments in the insert method.

• The first argument specifies the position – where to add the column.
• It’s a 0-based index, so we provided 2 to add the column after the ID column.
• Then we provided the column name and the last argument contains the values for the new column.

Python program:

import pandas as pd

inflation_data = {

  "Year": [2015, 2016, 2016, 2017],

  "Inflation": ['1.75%', '2%', '3%', '3.5%']

}


#Creating a Data frame with two columns

df_inf = pd.DataFrame(inflation_data)


#Adding a new column at second number in the DF

df_inf.insert(1, "Difference", [0.75, 0.25,1,0.5])


#Display Data Frame with new column

print(df_inf)

Output:

You can see, the “Difference” column is added after the first column “Year”.

The example of adding a duplicate column

As mentioned earlier, Python will generate an error if you try adding a column name that already exists.

See below where we used the insert method for adding a column “Name” in the above-created data frame.

Code:

import pandas as pd


inflation_data = {

  "Year": [2015, 2016, 2016, 2017],

  "Inflation": ['1.75%', '2%', '3%', '3.5%']

}


#Creating a Data frame with two columns

df_inf = pd.DataFrame(inflation_data)



#Adding a new column at second number that already exist

df_inf.insert(1, "Year", [2018,2019,2020,2021])

#Display Data Frame with new column

print(df_inf)

Output:

So, it generated the ValueError.

Using allow_duplicates in the insert method

In order to allow adding a duplicate column, you may use the allow_duplicates argument as follows:

See the same example as above and the output.

Code:

import pandas as pd

inflation_data = {

  "Year": [2015, 2016, 2016, 2017],

  "Inflation": ['1.75%', '2%', '3%', '3.5%']

}


#Creating a Data frame with two columns

df_inf = pd.DataFrame(inflation_data)


#Adding a new column at second number that already exist with allow_duplicates=True

df_inf.insert(1, "Year", [2018,2019,2020, 2021], allow_duplicates=True)


#Display Data Frame with new column

print(df_inf)

Output: