Скачать или смотреть How to Reverse Sort a List in Python While Preserving Order

Learn how to reverse sort a list in Python, preserving the original order of the same numbers while prioritizing specific items!
---
This video is based on the question https://stackoverflow.com/q/63991056/ asked by the user 'Chang Zhao' ( https://stackoverflow.com/u/9567948/ ) and on the answer https://stackoverflow.com/a/63995235/ provided by the user 'Ciasto piekarz' ( https://stackoverflow.com/u/3311276/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: reverse sorting a list preserving the order of the same number

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Reverse Sort a List in Python While Preserving Order

Sorting lists is a common task in programming, but what happens when you need to sort a list in reverse order while ensuring that certain items take precedence? In this guide, we will tackle a specific challenge: reverse sorting a list of numbers while ensuring items tagged with '(key)' appear first.

Let’s break down the problem and find a solution step by step.

Understanding the Problem

You have a list that consists of numbers, some of which have an additional text label, '(key)'. Here's an example of the list:

[[See Video to Reveal this Text or Code Snippet]]

Desired Output

The goal is to reverse sort this list while ensuring that any numbers associated with '(key)' appear before the same number without the tag. The expected result for the above list is:

[[See Video to Reveal this Text or Code Snippet]]

Why Traditional Sorting Doesn’t Work

Using Python's built-in sort() method with reverse=True would not give you the desired output. For instance, it would result in:

[[See Video to Reveal this Text or Code Snippet]]

As you can see, the sorting ignores the position of (key) items, simply ordering them based on the string values.

Implementing the Solution

To achieve the desired output, we will implement a solution using a custom sorting method. Follow these steps:

Step 1: Grouping Elements

We will first group the elements into pairs:

The first element will be the number without the (key) tag.

The second element, if it exists, will be the number with the (key) tag.

Step 2: Sorting the Groups

Next, we will sort these groups in reverse order based on the first element of each pair.

Step 3: Building the New List

Finally, we will construct a new list by appending the items in the desired order: first the (key) element followed by the corresponding number.

Here’s how you can implement this in Python:

[[See Video to Reveal this Text or Code Snippet]]

Final Output

When you run the above code, you will see the desired:

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

Sorting lists in Python can sometimes present unique challenges, particularly when additional contextual information (like '(key)') is involved. By carefully grouping and sorting our data, we can effectively manage these cases. The solution we’ve discussed ensures that we prioritize (key) items while maintaining the numerical order as intended.

Feel free to try this out with different lists and see how it can be adapted for your needs!