How to Merge and Sum Dictionary Values in Python

Learn how to effectively `merge and sum` values from multiple Python dictionaries while preserving keys using only the standard library.
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How to Merge and Sum Dictionary Values in Python

Merging and summing dictionary values in Python can be a common task, especially when working with data that requires aggregation. Suppose you have multiple dictionaries containing similar keys but varying values for those keys. The challenge is to combine these dictionaries such that for keys that are identical, their values are summed up, while also preserving the values from unique keys in the dictionaries. In this guide, we will explore a practical method to achieve this with Python's standard library.

Understanding the Problem

Consider the following two dictionaries:

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We want to merge these dictionaries so that the output looks like this:

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In this desired output:

The values for key 'A' in both dictionaries are summed where the inner keys are the same.

The unique keys (like 'd' in dictionary 2) are simply added to the merged dictionary without any changes.

Step-by-Step Solution

To solve this problem, we can follow these steps:

1. Initialize an Output Dictionary

Start by creating an empty dictionary that will hold our merged result.

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2. Iterate through Each Dictionary

Go through each dictionary in your list of dictionaries, processing one at a time.

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3. Check for Existing Keys

For each dictionary, iterate through its keys, checking if the key already exists in the output dictionary. If it does not, create a new dictionary for that key.

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4. Sum the Values of Inner Dictionary Keys

Within each key, also iterate through its inner dictionary keys. Here you will check if the inner key already exists in the output dictionary.

If it does exist, sum the values.

If it does not, just assign the value directly.

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5. Putting It All Together

Here’s the complete code that accomplishes the above steps:

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

Conclusion

This method allows you to merge and sum dictionary values effectively using basic loops and conditional checks. It is essential to note that this solution relies solely on Python's standard library, making it accessible for any Python environment. You can easily adapt this code to handle more dictionaries by simply extending the dicts list.

Now you can aggregate your dictionaries with confidence, ensuring that you retain all the necessary data while maintaining accuracy in your sums!