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Learn how to effectively combine two lists in Python, where the items in the second list repeat according to the values in the first list, using simple Python techniques.
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This video is based on the question https://stackoverflow.com/q/73303319/ asked by the user 'Duvan Smuts' ( https://stackoverflow.com/u/19602042/ ) and on the answer https://stackoverflow.com/a/73303420/ provided by the user 'Tim Biegeleisen' ( https://stackoverflow.com/u/1863229/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Combine Two Lists with Repetitions Based on Another List in Python

If you've been working with lists in Python, you might find yourself wanting to combine two lists in a dynamic way. A common scenario is when you have two lists of the same size, and you want the elements of the second list to repeat based on the corresponding numbers from the first list. Let’s explore how to achieve this using a straightforward method in Python.

The Problem

Suppose you have two lists:

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

Each element in list1 tells you how many times you wish to repeat the corresponding element from list2. For example, the first element in list1 is 5, which means that the first element in list2 (29888.20) should appear 5 times in the final output list. The objective here is to create a new list where each number from list2 appears as many times as specified by list1.

The Solution

The problem can be elegantly solved using list comprehension in Python. Here's a breakdown of the solution.

Steps to Combine the Lists

Zip the Lists Together: This function pairs each element from list1 with the corresponding element in list2.

Repeat the Second List Items: For each pair, repeat the value from list2 according to the number specified in list1.

Flatten the List: The result will be a list of lists, so we will use another list comprehension to flatten it into a single list.

Code Implementation

Here’s how you can write the complete code:

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

Output

When you run the above code, the output will be:

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

Breakdown of the Code

List Comprehension:

The inner part [[y]*x for x, y in zip(list1, list2)] creates a list where every y from list2 is repeated x times from list1.

The outer part for j in sub flattens the resulting list of lists into a single list.

Understanding the Output

The output list reflects the requirements where each number from list2 appears exactly as many times as defined by the corresponding number in list1.

For example, 29888.20 appears 5 times, 34298.20 appears 20 times, and so on as required.

Conclusion

Combining two lists with dynamic repetitions based on values from another list is a powerful technique in Python. Utilizing zip() along with list comprehensions not only provides a clear and concise solution but also takes full advantage of Python's expressive capabilities. With this approach, you can manipulate lists in a way that is both efficient and easy to understand.

Feel free to experiment with different values in list1 and list2 to see how the output changes. Happy coding!