Unique Elements

Prompt

Write a function that takes an array as input and returns a new array containing only the unique elements (removing all duplicates).

Your solution should maintain the original order of elements, keeping the first occurrence of each element and removing subsequent duplicates.

Program your solution in JavaScript and provide a concise explanation of your approach.

Playground

Solution

Explanation

There are multiple ways to filter unique elements from an array in JavaScript:

Solution 1: Using Set

The most concise solution uses the Set object, which only stores unique values. By converting the array to a Set and then back to an array using the spread operator, we get an array of unique elements:

return [...new Set(arr)];

This solution is elegant and efficient with O(n) time complexity. It also correctly handles special values like NaN, which are considered equal in a Set.

Solution 2: Using filter()

Another approach is to use the filter() method combined with indexOf():

return arr.filter((item, index) => arr.indexOf(item) === index);

This keeps an element only if its current index matches the first index it appears in the array. This solution has O(n²) time complexity because indexOf() performs a linear search for each element.

Solution 3: Manual Tracking

For more complex cases or better performance with large arrays, we can manually track elements we've seen:

const result = [];
const seen = {};
for (const item of arr) {
  const key = typeof item + JSON.stringify(item);
  if (!seen[key]) {
    result.push(item);
    seen[key] = true;
  }
}
return result;

This solution has O(n) time complexity and works well for most cases, though the serialization approach may have limitations with complex objects.

The Set-based solution (Solution 1) is generally preferred for its simplicity and efficiency unless there are specific requirements that necessitate a different approach.

[...new Set(arr)]