Resolving the Issue of Matrix Mutation in JavaScript with Array.fill()

Discover why modifying a matrix initialized with `Array.fill()` affects the entire column and learn the correct approach to create an independent matrix in JavaScript.
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This video is based on the question https://stackoverflow.com/q/66623300/ asked by the user 'Ionut Eugen' ( https://stackoverflow.com/u/9398337/ ) and on the answer https://stackoverflow.com/a/66623360/ provided by the user 'Nenad Vracar' ( https://stackoverflow.com/u/4620771/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Matrix Initialization in JavaScript

When working with multi-dimensional arrays, or matrices, in JavaScript, developers often run into some peculiar behavior. One common problem arises during initialization, especially when using the Array.fill() method. In this guide, we will explore a specific issue: modifying the value of a matrix filled with Array.fill() modifies the entire column!

The Problem Explained

Consider the following scenario:

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

When you initialize a matrix A of dimensions n*n using Array.fill(), you might expect each row to contain unique arrays. However, the output reveals a frustrating truth: when you change a value, it inadvertently modifies all other rows in that specific column.

Why Does This Happen?

This unexpected behavior occurs because:

The first Array.fill() call is filling the outer array with the same inner array reference.

Consequently, all rows refer to the exact same inner array. Thus, any modification to one of them affects all.

The Solution: Using Array.from()

To avoid this problem, we need to create distinct inner arrays for each row instead of referencing the same one. Let's see how we can achieve this using Array.from().

Updated Initialization Code

Replace the original matrix initialization with the following code:

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

Breakdown of the Solution

Array Creation:

Array.from(new Array(n), ...) creates a new array with n elements.

The second argument, a mapping function, is executed for each slot in the outer array.

Inner Array Definition:

() => new Array(n).fill(0) generates a new inner array filled with zeros for each row. This ensures that each row is a unique array in memory.

Benefits of This Approach

Independent Rows: Each row in the matrix is a separate instance, meaning changes to one row do not affect others.

Maintainability: The code is easier to read and understand, allowing for better collaboration and troubleshooting.

Conclusion

Initializing a matrix in JavaScript requires careful consideration to avoid pitfalls with references. By understanding how Array.fill() works and switching to Array.from(), we can create matrices whose columns exhibit the intended behavior.

Apply this knowledge in your coding practices to manage multi-dimensional arrays effectively!

Feel free to reach out with questions or share your experiences in managing arrays in JavaScript. Happy coding!

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