Скачать или смотреть How to Iterate Through a List and Combine Values by Matching Signs in Python

Learn how to iterate through a list in Python, checking values for matching signs and combining them into a new list. This guide provides a clear step-by-step solution to a common programming problem.
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How to Iterate Through a List and Combine Values by Matching Signs in Python

When working with lists in Python, there might be cases where you want to analyze numerical data based on certain conditions. A common challenge is iterating through a list of values to identify sequences based on their signs (positive or negative). In this guide, we'll explore a solution for combining adjacent values in a list that share the same sign while ensuring their order is preserved. Let's dive into the problem and see how we can efficiently solve it using Python.

The Problem

Imagine you have a list of integers that contains both positive and negative values. For example:

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Your goal is to iterate through this list and sum up adjacent numbers that share the same sign (+ or -) until you reach a number that has the opposite sign. The expected outcome for our example list would be:

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Here's the breakdown of how we achieve this:

The first three numbers (1, 2, 1) are positive and are summed to get 4.

The next two numbers (-1, 2) do not share a sign, so they're simply appended to the output list.

The same logic follows through the rest of the list.

The Solution

To tackle this problem, we will leverage a while loop to iterate through the list. We'll maintain a current sum that accumulates values until we encounter a number with a different sign. Let's break down the solution into clear steps.

Step 1: Initialize Variables

First, we need to set up our list and an empty list where we will store the combined values.

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Step 2: Outer While Loop

We use an outer while loop to go through each element in the list. It's important to ensure that we don’t exceed the list's length.

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In this step, we set the current sum to the current element and increment the index.

Step 3: Inner While Loop

Next, we introduce an inner while loop that checks whether the current number retains the same sign as the previous numbers.

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This will keep accumulating the sum if the next number shares the same sign. Once we reach a number with a different sign or the end of the list, we exit the inner loop.

Step 4: Append to Data List

Finally, once we exit the inner loop, we append the current sum to our output list.

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Complete Code

Now that we have our plan down, here is the complete code to achieve our goal:

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When you run the above code, it will yield the desired output of [4, -1, 2, -1, 2, -4, 4].

Conclusion

This method allows you to effectively iterate through a list, summing values based on their signs while maintaining the order of the elements. Understanding how to manage loops and conditions in Python is a fundamental skill that can help you with a variety of more complex problems. Next time you face a similar challenge, refer back to this solution for guidance. Happy coding!