lodash: Get duplicate values from an array

var array = [1, 1, 2, 2, 3];
var groupped = _.groupBy(array, function (n) {return n});
var result = _.uniq(_.flatten(_.filter(groupped, function (n) {return n.length > 1})));

This works for unsorted arrays as well.

You can use this:

_.filter(arr, (val, i, iteratee) => _.includes(iteratee, val, i + 1))

Note that if a number appears more than two times in your array you can always use _.uniq.

How about using countBy() followed by reduce()?

const items = [1,1,2,3,3,3,4,5,6,7,7];

const dup = _(items)
    .countBy()
    .reduce((acc, val, key) => val > 1 ? acc.concat(key) : acc, [])
    .map(_.toNumber)

console.log(dup);
// [1, 3, 7]

http://jsbin.com/panama/edit?js,console

Another way is to group by unique items, and return the group keys that have more than 1 item

_([1, 1, 2, 2, 3]).groupBy().pickBy(x => x.length > 1).keys().value()