How to Add a New Column to an Existing Pandas DataFrame in Python

This tutorial will explain several ways to add new columns to an existing DataFrame in Pandas with code examples.

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Using DataFrame.insert()

We can use the DataFrame.insert() method to insert a column at any position in the DataFrame.

import pandas as pd

data = {'Name': ['electron', 'muon', 'proton', 'neutron'],
'Mass': [0.511, 105.7, 938.3, 939.6],
'Charge': [-1, -1, 1, 0]}

df = pd.DataFrame(data)

print(df)

      Name     Mass  Charge
0  electron    0.511      -1
1      muon  105.700      -1
2    proton  938.300       1
3   neutron  939.600       0

df.insert(3, 'Spin', [1/2, 1/2, 1/2, 1/2], True)

print(df)

     Name     Mass  Charge  Spin
0  electron    0.511      -1   0.5
1      muon  105.700      -1   0.5
2    proton  938.300       1   0.5
3   neutron  939.600       0   0.5

Using DataFrame.assign()

We can use the DataFrame.assign() method to assign one or more columns to an existing DataFrame. The assign method will create a new DataFrame with the new columns added to the existing DataFrame.

import pandas as pd

data = {'Name': ['electron', 'muon', 'proton', 'neutron'],
'Mass': [0.511, 105.7, 938.3, 939.6],
'Charge': [-1, -1, 1, 0]}

df = pd.DataFrame(data)

print(df)

      Name     Mass  Charge
0  electron    0.511      -1
1      muon  105.700      -1
2    proton  938.300       1
3   neutron  939.600       0

df2 = df.assign(Spin=[1/2, 1/2, 1/2, 1/2])

print(df2)

     Name     Mass  Charge  Spin
0  electron    0.511      -1   0.5
1      muon  105.700      -1   0.5
2    proton  938.300       1   0.5
3   neutron  939.600       0   0.5

Declaring New List as a Column

We can add a new list as a column to an existing DataFrame as follows:

import pandas as pd

data = {'Name': ['electron', 'muon', 'proton', 'neutron'],
'Mass': [0.511, 105.7, 938.3, 939.6],
'Charge': [-1, -1, 1, 0]}

df = pd.DataFrame(data)

print(df)

spin = [1/2, 1/2, 1/2, 1/2]

df['Spin'] = spin

print(df)

       Name     Mass  Charge
0  electron    0.511      -1
1      muon  105.700      -1
2    proton  938.300       1
3   neutron  939.600       0

       Name     Mass  Charge  Spin
0  electron    0.511      -1   0.5
1      muon  105.700      -1   0.5
2    proton  938.300       1   0.5
3   neutron  939.600       0   0.5

Summary

Congratulations on reading to the end of this tutorial. The AttributeError: ‘DataFrame’ object has no attribute ‘concat’ occurs when you try to call the concat method on a DataFrame instead of using the built-in Pandas method.

For further reading on errors related Pandas, go to the articles:

• How to Solve Python AttributeError: ‘Series’ object has no attribute ‘lower’.
• How to Solve Python AttributeError: ‘DataFrame’ object has no attribute ‘unique’

To learn more about Python for data science and machine learning, go to the online courses page on Python for the most comprehensive courses available.

Have fun and happy researching!