How to Get Sorted Indices of a List of Lists in Python

Learn how to retrieve the indices of elements in a sorted list of lists in Python. This guide covers techniques using both lists and numpy arrays.
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How to Get Sorted Indices of a List of Lists in Python: A Simple Guide

When working with lists in Python, especially lists of lists (a common data structure), it can often be tricky to derive useful information like sorted indices. For instance, you may have a list of lists containing numerical values and wish to know the original indices of those values once they are sorted in increasing order.

In this post, we will explore how to achieve this with a clear example, along with step-by-step instructions. This technique can be particularly useful in data manipulation and analysis scenarios.

Problem Overview

Consider the following list of lists named test:

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

Your goal is to determine the indices of the merged elements (i.e., 1, 2, 3, 4) when they are sorted. For this example, the desired output should be:

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

Where:

[0, 0] corresponds to the element 1 (first element in the first list).

[0, 1] corresponds to the element 2 (second element in the first list).

and so on.

Solution Approach

To obtain the sorted indices of elements from a list of lists, we can utilize Python's enumerate function along with sorting capabilities. We will break down the process into easy-to-follow steps.

Step-by-Step Solution

Flatten the List: We need to create a list where each entry corresponds to the value and its index.

Sort the List: After flattening, we can sort the list of tuples based on the values.

Extract the Indices: Finally, we'll extract the indices to obtain our desired output.

Implementation

Here's how you can implement the above steps in Python:

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

When you run this code, it produces:

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

Explanation of Code

List Comprehension: The code uses list comprehension to create a new list of tuples. Each tuple contains:

The value of the element.

Its respective indices in the format [i, j].

Sorting: The sorted() function sorts the flattened list based on the first element of each tuple (the values).

Extracting Indices: In the final step, we reconstruct the indices in the required format and print the output.

Conclusion

Using the outlined method, you can easily retrieve the indices of sorted elements from a list of lists in Python. This technique is not only straightforward but also efficient, making it a great addition to your programming toolkit.

Consider experimenting with different lists and structures to fully grasp the concept.

Happy coding!