Can a Boolean Comparison Function Properly Sort a JavaScript Array?

Sorting in JavaScript: Isn't Returning a Boolean Sufficient for a Comparison Function?

The traditional way of sorting an array in JavaScript is by using the Array.sort() method, which allows you to specify a custom comparison function.

Question:

Can we simply use a boolean comparison function (returning true/false) to sort an array, or do we need to return a numeric value (e.g., 1, -1, 0)?

Answer:

No, returning a boolean is not sufficient for a comparison function in JavaScript. The comparison function must return a numeric value indicating the relationship between the two elements being compared:

• 1 if a is greater than b
• -1 if a is less than b
• 0 if a is equal to b

Reasoning:

Returning a boolean only specifies whether one element is greater or less than the other, but it doesn't provide enough information for the sorting algorithm to determine which element comes first. For instance, a comparison function returning true does not specify whether a is just greater than b or much greater than b.

Why the Wrong Solution is Prevalent:

The incorrect solution of returning a boolean is prevalent because it works in some cases, especially when sorting simple arrays of numbers. However, it can lead to unexpected results when sorting more complex data or when using unstable sorting algorithms (which alter the ordering of equal elements).

Correct Comparison Functions:

To sort an array correctly, use one of the following comparison functions:

• Lexicographic Sort (No Comparison Function): For a simple lexicographic sort, don't provide a comparison function. The items will be stringified and sorted accordingly.

• Generic Comparison Function:

  function(a, b) {
    if (a > b) return 1;
    if (a < b) return -1;
    /* else */ return 0;
  }

• Comparison Function for Numbers:

  function(a, b) {
    return a - b;
  }

Note:

• Always ensure that your comparison function is consistent and follows the rules of transitivity to avoid unexpected sorting behavior.
• For sorting composite types, modify the comparison function to compare the desired properties or use a custom function that returns a sortable value.

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