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

title
Diff Two Arrays

Remember to use Read-Search-Ask if you get stuck. Try to pair program and write your own code

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)

Hint: 1

Merge the list to make it easy to compare functions.

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Hint: 2

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

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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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Spoiler Alert!

Solution ahead!

Basic Code Solution (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]);

Run Code

Code Explanation:

Read the comments in the code.

Relevant Links

• for Loop (Devdocs)

Intermediate Code Solution (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]);

Run Code

Code Explanation:

Explain solution here and add any relevant links

Relevant Links

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

Advanced Code Solution (Declarative Solution):

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

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

Run Code

Code Explanation:

Explain solution here and add any relevant links

Advanced Code Solution Alternative (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)

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See Wiki Challenge Solution Template for reference.