So for ex. I have this array with these values :

let arr = [1, 2, 3, 3, 3, 4, 4];

How can I get a new arr as :

let newArr = [3, 3, 4, 4];

while at the same time the original array should be changed as :

let arr = [1, 2, 3];

one 3 is left behind cause there is only one pair of 3.

I tried this code below ( a for loop & splice ) but it is not working properly.

let result = [];

for (let i = 0; i < sorted.length; i  ) {
    if (sorted[i] === sorted[i   1]) {
        let pair = sorted.splice(i, 1);
        pair.forEach(el => result.push(el));
    }
}

CodePudding user response：

Few things corrected,

1. You need to splice two items from the point you see duplicates. Try like this.
2. Iteration stop condition should be i < sorted.length - 1 as we consider two consecutive items.
3. Use Array.prototype.concat to join duplicates to the result array.

let sorted = [1, 2, 3, 3, 3, 4, 4];
let result = [];

for (let i = 0; i < sorted.length - 1; i  ) {
    if (sorted[i] === sorted[i   1]) {
        let pair = sorted.splice(i, 2);
        result = result.concat(pair)
    }
}

console.log(sorted)
console.log(result)

CodePudding user response：

Thanks Sebastian Simon, it working now.

 for (let i = 0; i < sorted.length; i  ) {
    if (sorted[i] === sorted[i   1]) {
        let pair = sorted.splice(i, 2);
        pair.forEach(el => result.push(el));
        i--;
    }
}