How to Populate a Dictionary of Lists Using Comprehension in Python

Discover an elegant way to structure data in Python by using comprehensions to create a dictionary of lists from a list of 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: How to populate a dictionary of lists using comprehension?

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Populate a Dictionary of Lists Using Comprehension in Python

When working with data in Python, developers often need to convert lists of dictionaries into a more structured format. One common task is populating a dictionary where each key corresponds to a list of values. In this guide, we will tackle the question: How to populate a dictionary of lists using comprehension?

The Problem

Imagine you have the following source list of dictionaries:

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

Your goal is to transform this list into a dictionary that looks like this:

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

While one might construct this dictionary using a nested loop like the following:

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

This code effectively gets the job done but may feel a bit clumsy. So, let's explore a more elegant approach using dictionary comprehension in Python.

The Solution

Using Dictionary Comprehension

We can create our desired dictionary using a concise comprehension. The following code demonstrates how to achieve this:

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

Explanation of the Code

Initialization of the Dictionary: We start by initializing an empty dictionary d.

Iterating Over Keys: We iterate over the predefined keys ['I', 'R']. This can be modified to include any set of keys as required.

List Comprehension: For each key k, we use a list comprehension to populate the dictionary:

The comprehension iterates over each dictionary d_ in the source list s.

It checks if the current key k is present in d_.

If it is, it pulls the value associated with that key and appends it to the list for the current key in the new dictionary.

Dynamically Determining Keys

If you want to avoid hardcoding the keys, you can dynamically determine them like this:

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

Steps Involved Here:

Using a Set Comprehension: The keys are determined by extracting the keys from each dictionary in the list and converting them into a set, which handles duplicates efficiently.

Remaining Logic: The remaining logic stays the same — we construct the values based on the keys found in the dictionaries.

Conclusion

Using comprehension not only makes your code cleaner but also enhances its readability. By using the method we discussed, you can efficiently create a dictionary of lists without resorting to lengthy and repetitive loops. This practice is especially helpful when you’re managing larger datasets in Python, streamlining data manipulation significantly.

Give it a try with your own source lists of dictionaries, and watch how easily you can transform your data structures!