Pandas DataFrame: How to change data type of a column

Updated: February 20, 2024 By: Guest Contributor Post a comment


When working with data in Python, Pandas is an indispensable library that provides high-level data structures and wide variety tools for data analysis. One of the frequent operations while working with Pandas DataFrames is modifying the data type of columns. Changing the data type of a column is essential for numerous reasons such as optimizing memory usage, ensuring compatibility with other Python libraries, or simply aligning with the data’s correct type for operations.

This tutorial will guide you through several methods to change the data type of a column in a Pandas DataFrame. We will start with basic examples and proceed to more advanced use cases, demonstrating each with code examples.

Understanding Data Types in Pandas

Before diving into changing column data types, it’s crucial to understand the different data types available in Pandas:

  • Numeric Types: int (integer), float (floating point number)
  • Object Types: typically strings (text) but can include mixed types
  • Datetime: for dates and times
  • Boolean: for True/False values
  • Category: for categorical values

Basic Conversion Methods

To start, let’s look into basic types of data type conversion in Pandas. Suppose we have the following DataFrame:

import pandas as pd

data = {'Name':['John', 'Anna', 'Peter', 'Linda'],
        'Age':['30', '29', '24', '28'],
        'Salary':[50000, 54000, 32000, 59000]}
df = pd.DataFrame(data)

ThisDataFrame shows that while ‘Age’ should be an integer, it is currently saved as an object (string). Let’s change ‘Age’ to an integer:

df['Age'] = df['Age'].astype(int)

The output demonstrates that the ‘Age’ column is now correctly identified as an integer type.

Using to_numeric Function

For converting strings that represent numbers to a numeric datatype, you can use pd.to_numeric():

df['Salary'] = pd.to_numeric(df['Salary'], errors='coerce')

Here, errors='coerce' makes sure that if there’s any error during conversion (e.g., a value that cannot be converted to a number), that specific value will be replaced with NaN (not a number).

Advanced Conversion Techniques

As we delve deeper, let’s explore more sophisticated methods for data type conversion.

Converting to DateTime

If you’re dealing with columns that contain date or time information, converting them to datetime is crucial for performing time-series analysis. Suppose you have a DataFrame with a ‘Date’ column in string format:

df['Date'] = pd.to_datetime(df['Date'])

This simple conversion facilitates working with dates in a multitude of ways, such as filtering data by date, extracting parts of the date (year, month, day), and more.

Handling Categories

When working with data that has a limited, fixed number of unique values (e.g., gender, country, product categories), converting these to a ‘category’ datatype can significantly reduce memory usage and speed up operations:

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

Categorical data is much more memory-efficient than object types for these use cases.

Custom Conversion Functions

Sometimes, direct conversion methods may not suit your needs, especially when performing complex conversions. In such cases, applying a custom function to change the data type of a column can be extremely powerful. For instance, converting a complex string pattern into a comprehensible format:

def custom_conversion(value):
    # Implement your conversion logic here
    return new_value

df['CustomColumn'] = df['CustomColumn'].apply(custom_conversion)

This method provides the flexibility to handle almost any data type conversion in a nuanced way, tailored to your specific dataset.


Changing the data type of a column in a Pandas DataFrame is a fundamental operation necessary for data cleaning, optimization, and preparation for analysis. We’ve explored various methods from simple type casting to advanced custom conversion functions. Applying these techniques appropriately will ensure that your data is in the right format, optimized for both memory usage and computational efficiency, laying down a strong foundation for any data analysis or machine learning project.