Remove duplicates in array

Question

This function sorts an array and returns the unique items. I'm trying to get it down to a readable 5 lines of code. So far I've renamed the variable cursor variable and inlined the assignments. I'll appreciate fresh eyes.

Before

function uniques(array) {
    var result = [], val, ridx;
    outer:
    for (var i = 0, length = array.length; i < length; i++) {
        val = array[i];
        ridx = result.length;
        while (ridx--) {
          if (val === result[ridx]) continue outer;
        }
        result.push(val);
    }
    return result;
}

After

function uniques(array) {
    var result = [], val, cursor;
    outer:
        for (var i = 0, length = array.length; i < length; i++) {
        val = array[i], cursor = result.length;
        while (cursor--) {
          if (val === result[cursor]) continue outer;
        }
        result.push(val);
    }
    return result;
}

Answer 1

This function sorts an array and returns the unique items

1. Remove duplicates from the array using Array#filter
2. Sort the array using Array#sort

Code:

function uniques(arr) {
    // Remove the duplicate elements from the array
    return arr.filter(function (element, index, arr) {
        return arr.indexOf(element) === index;
    }).sort(function (a, b) {
        return a - b;
    });
}

Answer 2

This can be done as a 1 liner:

function uniques(arr) {
  return arr.sort().filter(function(x,i) { return x !== arr[i+1] });
}

All we're doing is sorting, then using filter to remove any element that is equal to its next adjacent element. Because the array is already sorted, it's guaranteed that duplicates will be next to one another.

Also note that this will run in O(n log n) time, and so will be faster than Tushar's answer, which filters first and then sorts -- the filtering step there will be O(n^2) because of the call to indexOf.

Finally, the above solution mutates the orginal array. If you'd like avoid that, simply add in a slice:

function uniques(arr) {
  return arr.slice(0).sort().filter(function(x,i) { return x !== arr[i+1] });
}