When using array.filter(), falsey values are excluded in a function expression, however, they are not excluded when using an arrow function

Question

When using array.filter(), falsey values are excluded in a function expression, however, they are not excluded when using an arrow function

Currently, I'm tackling a challenge that involves the array_diff function, which aims to retrieve values from array a that also exist in array b.

Having recently learned about the advantages of named function expressions for console debugging over anonymous fat arrow functions, I decided to approach this problem by creating a named function called removeDuplicate to filter my array.

Despite my efforts, I've encountered an issue where the filter function unintentionally eliminates the falsey value 0 from the output array.

This is the structure of the named function expression:

function array_diff(a, b) {
  return a.filter(function removeDuplicate(x) { if(b.indexOf(x) == -1) return x; });
}

array_diff([0,1,2,3,4],[2,4]); // [1, 3]

And here is the same logic implemented using an Anonymous Fat Arrow function:

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

array_diffTwo([0,1,2,3,4],[2,4]); // [0, 1, 3]

I'm seeking clarification on why the falsey value 0 gets removed in array_diff but not in array_diffTwo. Any insights would be greatly appreciated!

javascript arrays ecmascript-6 arrow-functions function-expression

Answer 1

Answer №1

The issue lies in the fact that when you use return x in the filter callback, if x (the current item being processed) evaluates to falsey, it will not be included in the final array, regardless of whether the condition b.indexOf(x) == -1 is met or not.

To rectify this problem, follow the same approach as shown below:

return b.indexOf(x) == -1

function array_diff(a, b) {
  return a.filter(function removeDuplicate(x) { return b.indexOf(x) === -1 });
}

console.log(array_diff([0,1,2,3,4],[2,4])); // [0, 1, 3]

(On another note, arrow functions are not used in the code snippet provided)

To optimize the computational complexity from O(n^2) to O(n), consider creating a Set of values from array b instead of repeatedly checking for indexOf on every iteration:

function array_diff(a, b) {
  const bSet = new Set(b);
  return a.filter(function removeDuplicate(x) { return !bSet.has(x); });
}

console.log(array_diff([0,1,2,3,4],[2,4])); // [0, 1, 3]

Answer 2

The issue lies in the fact that when you use return x in the filter callback, if x (the current item being processed) evaluates to falsey, it will not be included in the final array, regardless of whether the condition b.indexOf(x) == -1 is met or not.

To rectify this problem, follow the same approach as shown below:

return b.indexOf(x) == -1

function array_diff(a, b) {
  return a.filter(function removeDuplicate(x) { return b.indexOf(x) === -1 });
}

console.log(array_diff([0,1,2,3,4],[2,4])); // [0, 1, 3]

(On another note, arrow functions are not used in the code snippet provided)

To optimize the computational complexity from O(n^2) to O(n), consider creating a Set of values from array b instead of repeatedly checking for indexOf on every iteration:

function array_diff(a, b) {
  const bSet = new Set(b);
  return a.filter(function removeDuplicate(x) { return !bSet.has(x); });
}

console.log(array_diff([0,1,2,3,4],[2,4])); // [0, 1, 3]

Answer 3

Answer №2

There seems to be a misconception in how the array.filter(callback) method works. The callback should act as a predicate, where you return true for the elements you wish to keep and false for the ones you want to remove. By returning the elements themselves, it results in elimination of falsey elements.

Furthermore, an arrow function should look something like this:

array_diff =(a,b)=>a.filter(x=>b.indexOf(x)<0)
console.log(array_diff([0,1,2,3,4],[2,4]))

Answer 4

There seems to be a misconception in how the array.filter(callback) method works. The callback should act as a predicate, where you return true for the elements you wish to keep and false for the ones you want to remove. By returning the elements themselves, it results in elimination of falsey elements.

Furthermore, an arrow function should look something like this:

array_diff =(a,b)=>a.filter(x=>b.indexOf(x)<0)
console.log(array_diff([0,1,2,3,4],[2,4]))

When using array.filter(), falsey values are excluded in a function expression, however, they are not excluded when using an arrow function

Answer №1

Answer №2

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