pd Categofical astype('categorical')

Optimizing DataFrame Performance with Categorical Data Types

Optimizing DataFrame Performance with Categorical Data Types

While working with data in Python, one often encounters the need to store, manipulate, and analyze tabular data. The pandas library provides a powerful DataFrame object for this purpose. One of its less-discussed yet highly beneficial features is the support for categorical data types. Today, we will look at a simple example that demonstrates the advantages of converting a column to a categorical data type.

The Code Snippet

    exercises = ['pushups', 'squats','pullups ','jumping jacks'] * 2
    N = len(exercises)
    df = pd.DataFrame({'exercises':exercises,

    df['exercises'] = df['exercises'].astype('category')

Breaking Down the Code

Let's examine each section of this code to better understand its functioning.

Creating the Exercise List

The list of exercises, denoted by exercises, contains four types of exercises that are repeated twice, resulting in an eight-element list.

Setting Up the DataFrame

The code then defines a DataFrame named df that has three columns: exercise_id, exercises, and reps. It uses NumPy to generate random integers for the reps column.

Converting to Categorical

The last part of the code converts the exercises column to a categorical data type using astype('category').

Why Use Categorical Data Types?

Converting a column to a categorical type offers several benefits:

  • Memory Efficiency: Storing data as categorical types significantly reduces memory usage.
  • Performance: Categorical data types can lead to speedier operations.
  • Data Integrity: Limiting a column to a set of categories ensures that no erroneous data can be inserted.

Memory Efficiency

By default, string data in pandas is stored as object data types, which are memory-inefficient. When you convert these to categorical types, pandas uses integer-based encoding, dramatically reducing memory footprint.


Categorical types improve computational efficiency because operations like sorting or grouping can be performed faster on integer-based categories rather than string comparisons.

Data Integrity

By limiting the exercises column to a specific set of categories, you ensure data consistency. This helps prevent accidental insertion of incorrect or inconsistent data, thereby maintaining the integrity of your dataset.


The categorical data type is an invaluable feature in pandas, especially when dealing with repetitive or constrained string data. Although our example was straightforward, the implications for large, real-world datasets are significant. Leveraging the power of categorical types can make your data operations more efficient, your code cleaner, and your life easier. Google Colab Link


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