Replace duplicates items in array with different values

Question

i would like to Replace duplicates items with different values.
eg arr = [1,1,1,1,2,2,2,3] i want to replace the duplicates with R
So the result looks like this   arr = [1,R,R,R,2,R,R,3]
right now I'm using this approach:
    arr = [1,1,1,1,2,2,2,3]
    let previous = 0;
    let current = 1;
    while (current < arr.length) {
        if (arr[previous] === arr[current]) {
            arr[current] = 'R';
            current += 1;
        } else if (arr[previous] !== arr[current]) {
            previous = current;
            current += 1;
        }
    }

i wondering if there is different approach for to achieve that.  for Example  using Lodash (uniqwith, uniq).
Thanks

jonatjano · Answer

here's how I'd do it
It look if the current element is the first of the array with the current value and replace it if not
It may take some times on very big arrays


const input = [1,1,1,1,2,2,2,3]
let output = input.map(
  (el, i) => input.indexOf(el) === i ? el : 'R'
)
console.log(output)

Ernesto Stifano · Answer

This is actually very simple to do by using sets (Set).
const initialArray = [1,1,1,1,2,2,2,3];
const valuesSet = new Set();

const newArray = initialArray.map((value) => {
    if (valuesSet.has(value)) {
        return 'R';
    } else {
        valuesSet.add(value);
        return value;
    }
});

Nina Scholz · Answer

You could take a closure over a Set and check if the value is already seen or not.


let array = [1, 1, 1, 1, 2, 2, 2, 3],
    result = array.map((seen => v => seen.has(v) ? 'R' : (seen.add(v), v))(new Set));

console.log(...result);

A check previous value approach


let array = [1, 1, 1, 1, 2, 2, 2, 3],
    result = array.map((v, i, { [i - 1]: l }) => l === v ? 'R' : v);

console.log(...result);

Replace duplicates items in array with different values

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