How to Compare Two CSV Files and Extract Matching Entries in Python

Learn how to efficiently compare two CSV files in Python and extract matching entries into a new file. Step by step guide for beginner programmers.
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Comparing Two CSV Files in Python: A Step-by-Step Guide

When working with data, it's common to encounter situations where we need to compare two sets of information stored in CSV (Comma-Separated Values) files. One typical scenario is when we want to find matching entries based on specific criteria. In this post, we will explore how to compare two CSV files and extract matching entries into a third file using Python.

The Problem

Imagine you have two CSV files with the following structures:

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The Solution

To achieve this, we can break down the solution into several clear steps:

Step 1: Open the Files

First, we need to open the two files (file1 and file2) for reading and the output file (file3) for writing.

Step 2: Read and Compare Data

We will read the data from both files. For each row in file1, we will check for matching entries in file2 based on the first column values.

Step 3: Write Matching Entries

Instead of overwriting file3 every time we find a match, we should append to this file. This can be done by changing the file mode when opening file3 to "a+ ".

Complete Code Example

Here is a complete code example that implements the above logic:

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Explanation of the Code

File Opening: We use with open to handle file functionality safely.

Conclusion

By following these steps, you can effectively compare entries across two CSV files and extract the desired output into a new file. This method is particularly useful for data analysis or when managing large datasets where spotting similarities is crucial.

Happy coding, and don’t hesitate to dive deeper into Python’s csv module for more advanced functionalities!