freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/diff-two-arrays/index.md

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Diff Two Arrays

Diff Two Arrays

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Problem Explanation

Check two arrays and return a new array that contains only the items that are not in either of the original arrays.

Relevant Links

• for Loop (Devdocs)
• Array.prototype.includes (Devdocs)
• Array.prototype.filter (Devdocs)
• Array.prototype.concat (Devdocs)

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Hints

Hint 1

Merge the list to make it easy to compare functions.

Hint 2

Use filter to get the new array, you will need to create a callback function.

Hint 3

The best way to go about the callback function is to check if the number from the new merged array is not in both original arrays and return it.

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Solutions

Solution 1 (Click to Show/Hide)

(Imperative Solution)

function diffArray(arr1, arr2) {
  var newArr = [];

  function onlyInFirst(first, second) {
    // Looping through an array to find elements that don't exist in another array
    for (var i = 0; i < first.length; i++) {
      if (second.indexOf(first[i]) === -1) {
        // Pushing the elements unique to first to newArr
        newArr.push(first[i]);
      }
    }
  }

  onlyInFirst(arr1, arr2);
  onlyInFirst(arr2, arr1);

  return newArr;
}

diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]);

Code Explanation

Read the comments in the code.

Relevant Links

• for Loop (Devdocs)

Solution 2 (Click to Show/Hide)

(Declarative Solution):

function diffArray(arr1, arr2) {
  return arr1
    .concat(arr2)
    .filter(item => !arr1.includes(item) || !arr2.includes(item));
}

diffArray([1, 2, 3, 5], [1, 2, 3, 4, 5]);

Code Explanation

Explain solution here and add any relevant links

Relevant Links

• Array.prototype.concat (Devdocs)
• Array.prototype.filter (Devdocs)
• Array.prototype.includes (Devdocs)

Solution 3 (Click to Show/Hide)

(Declarative Solution)

function diffArray(arr1, arr2) {
  return [...diff(arr1, arr2), ...diff(arr2, arr1)];

  function diff(a, b) {
    return a.filter(item => b.indexOf(item) === -1);
  }
}

Relevant Links

• Array.prototype.includes (Devdocs)
• Array.prototype.filter (Devdocs)
• Array.prototype.concat (Devdocs)