How to Compare Two Lists by Index in Python

Описание: Learn how to create a Python function to compare two lists of names by index and determine if two people exchange gifts.
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This video is based on the question https://stackoverflow.com/q/65014707/ asked by the user 'FabriceDouceur' ( https://stackoverflow.com/u/3916671/ ) and on the answer https://stackoverflow.com/a/65014814/ provided by the user 'ombk' ( https://stackoverflow.com/u/13018113/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Compare Two Lists by Index in Python

In the world of programming, it's not uncommon to encounter problems that require you to work with data in lists. One such problem is the need to compare two lists and determine if elements at corresponding indices share a specific relationship. In this guide, we will dive into a particular scenario: comparing two lists of names to see if two individuals exchange gifts based on their respective positions in each list.

The Problem: Gift Exchange

Imagine you have two lists. The first list, L1, contains male names, while the second list, L2, contains female names — both are of equal length. The names at each index indicate who is giving a gift to whom; specifically, L1[k] gives a gift to L2[k]. Our goal is to create a function that returns True if there is any instance where a person gives a gift to someone who also gives a gift back to them.

Example

To give you an idea of what we are trying to achieve:

Lists:

L1 = ['A', 'B', 'C', 'D', 'E']

L2 = ['C', 'D', 'A', 'E', 'B']

In this case, the function should return True because:

A gives a gift to C (and C's index points to A in L1).

Conversely:

Lists:

L1 = ['A', 'B', 'C', 'D', 'E']

L2 = ['B', 'C', 'D', 'E', 'A']

Here, the function should return False since no one gives a gift back to the original givers.

The Solution: Writing the Function

Let's break down the solution. We need to write a function named compare that takes two lists as input: A and B, then evaluates if any pair in the lists meet the gift exchange condition.

Step-by-step Breakdown

Iterate Over the Length of the Lists:
We will use a for loop to iterate through the indices of the list.

Check for Gift Exchange:
For each index, verify if the corresponding elements from both lists are reciprocal.

Return Boolean Value:
If we find a match, we return True; otherwise, we continue checking until the end and finally return False.

The Implementation

Here is the complete implementation of the compare function:

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

Important Note

It's worth mentioning that this solution assumes both lists contain unique names. If there are duplicate names, this logic may not work as intended since A.index(B[i]) will only return the first occurrence of the name.

Conclusion

In this post, we tackled a compelling problem of comparing two lists by their indices and figured out if two people exchange gifts using a straightforward Python function. By understanding how to loop through the lists, check for matches, and return appropriate boolean values, you can solve similar issues with ease.

Keep practicing to improve your coding skills, and feel free to explore more complex list comparisons as you grow your Python knowledge.