JavaScript: Return the difference between two arrays

JavaScript fundamental (ES6 Syntax): Exercise-73 with Solution

Write a JavaScript program to return the difference between two arrays, after applying the provided function to each array element of both.

• Create a Set by applying fn to each element in b.
• Use Array.prototype.map() to apply fn to each element in a.
• Use Array.prototype.filter() in combination with fn on a to only keep values not contained in b, using Set.prototype.has().

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2
// Define a function 'differenceBy' to find the difference between two arrays based on a provided function.
const differenceBy = (a, b, fn) => {
  // Create a Set containing the result of applying the function 'fn' to each element of array 'b'.
  const s = new Set(b.map(v => fn(v)));
  // Filter array 'a' to keep only those elements for which the result of applying 'fn' is not present in Set 's'.
  return a.filter(x => !s.has(fn(x)));
};

// Example usage:
console.log(differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor)); // Outputs: [1.2]
console.log(differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x)); // Outputs: [{ x: 2 }]

Output:

[1.2]
[{"x":2}]

Flowchart:

Live Demo:

See the Pen javascript-fundamental-exercise-73 by w3resource (@w3resource) on CodePen.

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