let arrr = [7, 9, 30, 40, 50, 8, 1, 2, 3, 40, 90,2, 88,1];

output=[0, 1, 2, 3, 4, 5, 6, 7, 8 ,10, 12 ]

I saved this code at javascript playground here.

Question: I am trying to get all the index of unique elements in array. I have tried the code below to get the unqiue array but i do not know how to extract its index to give the expected output as above.

let ar = [1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 2, 1];
let unique = ar.filter((value, index) => {
  return ar.indexOf(value) == index;
});
console.log(unique);

CodePudding user response：

.indexOf() will always return the index of the first match. If we combine that with a Set we get the expected output:

let input = [7, 9, 30, 40, 50, 8, 1, 2, 3, 40, 90, 2, 88, 1];
const indices = input.map(el => input.indexOf(el));
const output = new Set(indices);
const output_as_array = [...output];  // if you need an actual array

console.log(output_as_array);

CodePudding user response：

1. Get all the unique values
2. Map over the uniques to use indexOf on the original array to get the indexes of the uniques

let arrr = [7, 9, 30, 40, 50, 8, 1, 2, 3, 40, 90,2, 88,1];
let unique = arrr.filter((v, i, a) => a.indexOf(v) === i);

let uniquesIndexes = unique.map(u => arrr.indexOf(u));
console.log(uniquesIndexes)

Output:

[
  0,
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  10,
  12
]