How to Sum Two Lists of Lists by First Index in Python

Learn how to elegantly sum two lists of lists by their first index in Python using dictionaries.
---

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: Sum list of list by first index

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Sum Two Lists of Lists by First Index in Python

Are you struggling to combine two lists of lists in Python by summing their first indices? This is a common task that many programmers encounter, whether they're working on data manipulation or processing tasks. In this guide, we'll walk you through an elegant solution to this problem, providing you with both a straightforward method and an alternative approach for summing these lists while keeping the code clean and efficient.

Understanding the Problem

Let's consider the example provided in the question. You have two lists of lists, L1 and L2:

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

Your goal is to sum the first elements of these inner lists when the second elements (the words) are the same. The desired output should look like this:

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

How can we efficiently accomplish this? Let's break it down into simple steps.

Solution Steps

The most straightforward way to achieve this is by using a dictionary to keep track of the accumulated values. Here's how you can do it:

1. Initialize a Dictionary

Start by creating an empty dictionary that will hold our summed values. The keys of the dictionary will be the words, and the values will be the summed scores.

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

2. Accumulate Counts

Next, traverse through both lists and accumulate the counts in the dictionary. You can use the setdefault method to simplify the adding process:

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

This function helps update the dictionary by adding the scores of the associated words.

3. Process Both Lists

Now, call this function for both L1 and L2:

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

4. Unpack the Dictionary

Once you have populated your dictionary with the scores, the final step is to convert the dictionary back into the desired list format:

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

Complete Code

Here is the full code encapsulated into a working function:

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

Conclusion

In this guide, we discussed an elegant method for summing two lists of lists by their first index using dictionaries in Python. This approach not only simplifies your code but also enhances readability and maintainability. Next time you encounter a similar problem, you can rely on this structured solution to guide you through the process.

By applying these techniques, you'll become more proficient in data manipulation with Python. Happy coding!