Скачать или смотреть How to Split a List into a Nested List in Python

Learn how to efficiently convert simple lists into complex nested lists in `Python` using an example-driven approach.
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This video is based on the question https://stackoverflow.com/q/67013301/ asked by the user 'Adil Husain Fida Ali' ( https://stackoverflow.com/u/15587312/ ) and on the answer https://stackoverflow.com/a/67027730/ provided by the user 'dyabmo' ( https://stackoverflow.com/u/15592162/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Split a List into a Nested List in Python

If you're working with data in Python and you have a list that needs to be transformed into a nested structure, you've likely encountered a challenge similar to the one below. For instance, consider you have a file that contains numerical data organized with hashtags as separators. Your goal is to read this data and store it in a nested list format. In this guide, we will walk you through the process of achieving this with a detailed example and step-by-step solution.

The Problem: Reading and Splitting a List

Imagine you have a text file named numerical.txt with the following content:

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Your objective is to convert this into a nested list, looking like this:

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However, starting with a basic implementation might yield a less organized output. For example:

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The resulting structure might appear like this:

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This is clearly not the format we want. Let's break down how to accomplish the desired output effectively.

The Solution: Step-by-Step Explanation

Step 1: Read the File

Start by opening the file for reading. As you process each line, you'll separate lines that contain data from those that contain hashtags.

Step 2: Initialize Lists for Results

Prepare two lists:

results: This will store the final nested list structure.

hashtag_results: This will temporarily hold the data between the hashtags.

Step 3: Loop Through Each Line

Loop through each line in the file and check whether it starts with a hashtag or contains numerical data.

Extracting Numerical Data:

If the line does not start with # , extract the numbers.

Split the line by the comma (,) and use list comprehension to convert them to floats.

Append the resulting list of floats to hashtag_results.

Handling Hashtags:

When encountering a hashtag and if hashtag_results is not empty, append hashtag_results to results, then reset hashtag_results to collect the next set of data.

Step 4: Final Append

After the loop, ensure that any remaining data in hashtag_results gets added to results.

Here’s the Complete Code

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Final Output

After running the above code, the output will be exactly what you need:

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Conclusion

Creating nested lists from flat data can be challenging, but with a clear approach and the right techniques, it can be accomplished smoothly in Python. By following the structured code and explanations provided above, you can transform any such structured data into a nested list as needed.

Happy coding, and don’t hesitate to share your own experiences with similar challenges in the comments below!