Python Pandas CategoricalIndex - Rename categories with lambda

To rename categories with Lambda, use the CategoricalIndex rename_categories() method in Pandas.

At first, import the required libraries −

import pandas as pd

CategoricalIndex can only take on a limited, and usually fixed, number of possible values. Set the categories for the categorical using the "categories" parameter. Treat the categorical as ordered using the "ordered" parameter −

catIndex = pd.CategoricalIndex(["P", "Q", "R", "S","P", "Q", "R", "S"], ordered=True, categories=["P", "Q", "R", "S"])

Display the CategoricalIndex −

print("CategoricalIndex...\n",catIndex)

Rename categories using rename_categories(). Set the new categories that with use lambda and set lowercase for all the categories −

print("\nCategoricalIndex after renaming categories...\n",catIndex.rename_categories(lambda a: a.lower()))

Example

Following is the code −

import pandas as pd

# CategoricalIndex can only take on a limited, and usually fixed, number of possible values
# Set the categories for the categorical using the "categories" parameter
# Treat the categorical as ordered using the "ordered" parameter
catIndex = pd.CategoricalIndex(["P", "Q", "R", "S","P", "Q", "R", "S"], ordered=True, categories=["P", "Q", "R", "S"])

# Display the CategoricalIndex
print("CategoricalIndex...\n",catIndex)

# Get the categories
print("\nDisplayingCategories from CategoricalIndex...\n",catIndex.categories)

# Rename categories using rename_categories()
# Set the new categories that with use lambda and set lowercase for all the categories
print("\nCategoricalIndex after renaming categories...\n",catIndex.rename_categories(lambda a: a.lower()))

Output

This will produce the following output −

CategoricalIndex...
CategoricalIndex(['P', 'Q', 'R', 'S', 'P', 'Q', 'R', 'S'], categories=['P', 'Q', 'R', 'S'], ordered=True, dtype='category')

DisplayingCategories from CategoricalIndex...
Index(['P', 'Q', 'R', 'S'], dtype='object')

CategoricalIndex after renaming categories...
CategoricalIndex(['p', 'q', 'r', 's', 'p', 'q', 'r', 's'], categories=['p', 'q', 'r', 's'], ordered=True, dtype='category')