How to Set Column as Index in a pandas DataFrame

In this tutorial, you will learn how to set a column as index in a DataFrame.

TLDR solution

# single column as index
df.set_index('column', inplace=True)

# Multiple column as index
df.set_index(['column_a', 'column_b'], inplace=True)

Step-by-Step Example

Suppose, you have a DataFrame on caught fish:

import pandas as pd

data = {'fish': ['salmon', 'pufferfish', 'shark'],
        'boat_id': [1, 2, 9],
        'count': [100, 10, 1],
        }   

df = pd.DataFrame(data)

print(df)

         fish  boat_id  count
0      salmon        1    100
1  pufferfish        2     10
2       shark        9      1

Set a Column as Index

You can boat_id as index using the set_index method. To replace the existing index set the inplace option to True.

df.set_index('boat_id', inplace=True)
print(df)

               fish  count
boat_id                   
1            salmon    100
2        pufferfish     10
9             shark      1

Set Multiple Column as Index

To set multiple columns as index in a DataFrame, simply input a list of columns:

import pandas as pd

data = {'fish': ['salmon', 'pufferfish', 'shark'],
        'boat_id': [1, 2, 9],
        'count': [100, 10, 1],
        }   

df = pd.DataFrame(data)

df.set_index(['boat_id', 'fish'], inplace=True)
print(df)

                    count
boat_id fish             
1       salmon        100
2       pufferfish     10
9       shark           1

That's it! You just learned how to set columns as index in a pandas DataFrame.