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JavaScript: Get all unique values of an array, based on a provided comparator function

JavaScript fundamental (ES6 Syntax): Exercise-108 with Solution

Write a JavaScript program to get all unique values of an array, based on a provided comparator function.

  • Use Array.prototype.reduce() and Array.prototype.some() for an array containing only the first unique occurrence of each value, based on the comparator function, fn.
  • The comparator function takes two arguments: the values of the two elements being compared.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2 
const uniqueElementsBy = (arr, fn) =>
  arr.reduce((acc, v) => {
    if (!acc.some(x => fn(v, x))) acc.push(v);
    return acc;
  }, []);

console.log(uniqueElementsBy(
  [
    { id: 0, value: 'a' },
    { id: 1, value: 'b' },
    { id: 2, value: 'c' },
    { id: 1, value: 'd' },
    { id: 0, value: 'e' }
  ],
  (a, b) => a.id == b.id
));

Sample Output:

[{"id":0,"value":"a"},{"id":1,"value":"b"},{"id":2,"value":"c"}]

Flowchart:

flowchart: Get all unique values of an array, based on a provided comparator function

Live Demo:

See the Pen javascript-basic-exercise-108-1 by w3resource (@w3resource) on CodePen.


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Previous: Write a JavaScript program to get all unique values (form the right side of the array) of an array, based on a provided comparator function.
Next: Write a JavaScript program to get the nth element of an given array.

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JavaScript: Tips of the Day

Returns an array of n-tuples of consecutive elements

Example:

const tips_arr = (n, arr) =>  n > arr.length ? [] : arr.slice(n - 1).map((v, i) =>[...arr.slice(i, i + n - 1), v]);
console.log(tips_arr(2, [1, 2, 3, 4, 5])); 
console.log(tips_arr(3, [1, 2, 3, 4, 5]));
console.log(tips_arr(5, [1, 2, 3, 4]));

Output:

[[1, 2], [2, 3], [3, 4], [4, 5]]
[[1, 2, 3], [2, 3, 4], [3, 4, 5]]
[]