JavaScript: Compute the union of two arrays

JavaScript Array: Exercise-22 with Solution

Write a JavaScript program to compute the union of two arrays.

Sample Data:
console.log(union([1, 2, 3], [100, 2, 1, 10]));
[1, 2, 3, 10, 100]

Visual Presentation:

Sample Solution:

JavaScript Code:

// Function to find the union of two arrays
function union(arra1, arra2) {
  // Check if either of the arrays is null, return undefined if true
  if ((arra1 == null) || (arra2 == null))
    return void 0;

  // Initialize an empty object to store unique elements from both arrays
  var obj = {};

  // Iterate through the elements of arra1 in reverse order
  for (var i = arra1.length - 1; i >= 0; --i)
    // Use each element as a key in the object to store unique values
    obj[arra1[i]] = arra1[i];

  // Iterate through the elements of arra2 in reverse order
  for (var i = arra2.length - 1; i >= 0; --i)
    // Use each element as a key in the object to store unique values
    obj[arra2[i]] = arra2[i];

  // Initialize an empty array to store the result (union)
  var res = [];

  // Iterate through the properties of the object
  for (var n in obj) {
    // Check if the property belongs to the object (not inherited)
    if (obj.hasOwnProperty(n))
      // Push the unique value to the result array
      res.push(obj[n]);
  }

  // Return the result array containing the union of the two input arrays
  return res;
}

// Output the result of the union function with sample arrays
console.log(union([1, 2, 3], [100, 2, 1, 10]));

Output:

[1,2,3,10,100]

Flowchart:

ES6 Version:

// Function to find the union of two arrays
const union = (arra1, arra2) => {
  // Check if either of the arrays is null, return undefined if true
  if ((arra1 == null) || (arra2 == null))
    return void 0;

  // Initialize an empty object to store unique elements from both arrays
  const obj = {};

  // Iterate through the elements of arra1 in reverse order
  for (let i = arra1.length - 1; i >= 0; --i)
    // Use each element as a key in the object to store unique values
    obj[arra1[i]] = arra1[i];

  // Iterate through the elements of arra2 in reverse order
  for (let i = arra2.length - 1; i >= 0; --i)
    // Use each element as a key in the object to store unique values
    obj[arra2[i]] = arra2[i];

  // Initialize an empty array to store the result (union)
  const res = [];

  // Iterate through the properties of the object
  for (let n in obj) {
    // Check if the property belongs to the object (not inherited)
    if (obj.hasOwnProperty(n))
      // Push the unique value to the result array
      res.push(obj[n]);
  }

  // Return the result array containing the union of the two input arrays
  return res;
};

// Output the result of the union function with sample arrays
console.log(union([1, 2, 3], [100, 2, 1, 10]));

Live Demo:

See the Pen JavaScript - Compute the union of two arrays - array-ex- 22 by w3resource (@w3resource) on CodePen.

Improve this sample solution and post your code through Disqus.

Previous: Write a JavaScript program to flatten a nested (any depth) array.
Next: Write a JavaScript function to find the difference of two arrays.