How to Calculate the Sum by Comparing Key Values in Two JavaScript Objects

Learn how to easily calculate the sum of values in JavaScript by comparing key values in two different objects. A step-by-step guide with examples.
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How to Calculate the Sum by Comparing Key Values in Two JavaScript Objects

In JavaScript, working with objects and calculating sums based on specific criteria can seem a bit daunting at first. However, it’s a common task, especially when dealing with data where you need to compare values across multiple objects. In this guide, we'll address a specific problem: how to calculate the sum of points based on answers retrieved from two objects. Let’s dive into an example and find out how to achieve this step by step.

The Problem

Imagine you have two objects:

values: This object contains questions (Q1, Q2) and their respective answers.

points: This object maps specific answers to their respective point values.

Here is what the data looks like:

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

You want to calculate the sum of points where the answer is "Yes". In this case, the expected result is 60 (41 from Q1A1 and 19 from Q2A1).

The Solution: Steps to Calculate the Sum

Method 1: Using reduce to Accumulate Sum

We can achieve this by using the reduce() method in JavaScript. Here's how:

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

Explanation:

reduce() is then used to iterate over this array, accumulating the sum of points based on matching conditions.

A nested reduce() goes through each entry of an answer and checks if the value is not 'No', and if the corresponding point exists in the points object.

If both conditions are met, it adds the points to the accumulator.

Method 2: Creating a Lookup Table

An alternative approach involves creating a lookup table for better readability. Here’s how you can do it:

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

Explanation:

We create a lookup object from the entries in values where the value is 'Yes'.

We then filter the points object to include only those entries whose keys are in the lookup object, summing their values using reduce().

Method 3: Collecting Keys and Calculating the Sum

Another straightforward approach involves collecting the keys of the answers you are interested in:

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

Explanation:

We gather the answer keys based on the entries in the values object.

Then we filter the points object looking for values that match our keys and sum those values.

Conclusion

Calculating sums based on comparisons of two objects in JavaScript can be performed with various methods. Depending on your preference for readability and maintainability, you can choose between using reduce() directly, creating a lookup object, or filtering keys. With a clear understanding of these methods, you can effectively manage and analyze data in your JavaScript applications.

Feel free to experiment with the methods shown above and choose the one that best fits your coding style! Happy coding!