How can I get a unique array based on object property using underscore

Question

I have an array of objects and I want to get a new array from it that is unique based only on a single property, is there a simple way to achieve this?

Eg.

[ { id: 1, name: 'bob' }, { id: 1, name: 'bill' }, { id: 1, name: 'bill' } ]

Would result in 2 objects with name = bill removed once.

Answer 1

Use the uniq function

var destArray = _.uniq(sourceArray, function(x){
    return x.name;
});

or single-line version

var destArray = _.uniq(sourceArray, x => x.name);

From the docs:

Produces a duplicate-free version of the array, using === to test object equality. If you know in advance that the array is sorted, passing true for isSorted will run a much faster algorithm. If you want to compute unique items based on a transformation, pass an iterator function.

In the above example, the function uses the objects name in order to determine uniqueness.

Answer 2

If you prefer to do things yourself without Lodash, and without getting verbose, try this uniq filter with optional uniq by property:

const uniqFilterAccordingToProp = function (prop) {
    if (prop)
        return (ele, i, arr) => arr.map(ele => ele[prop]).indexOf(ele[prop]) === i
    else
        return (ele, i, arr) => arr.indexOf(ele) === i
}

Then, use it like this:

const obj = [ { id: 1, name: 'bob' }, { id: 1, name: 'bill' }, { id: 1, name: 'bill' } ]
obj.filter(uniqFilterAccordingToProp('abc'))

Or for plain arrays, just omit the parameter, while remembering to invoke:

[1,1,2].filter(uniqFilterAccordingToProp())