filter-unique

When you need a Set but want to specify which keys should be used to determine "uniqueness".

Examples

Example data

const filterUnique = require('filter-unique');
const people = [
	{ birthDate: "2000-01-01", name: { first: "A", last: "A" } },
	{ birthDate: "2000-01-02", name: { first: "A", last: "A" } },
	{ birthDate: "2000-01-03", name: { first: "B", last: "B" } },
	{ birthDate: "2000-01-03", name: { first: "C", last: "B" } }
];

We only want the people with unique last names

let result = filterUnique(people, x => x.name.last);
/*
[
	{ birthDate: "2000-01-01", name: { first: "A", last: "A" } },
	{ birthDate: "2000-01-03", name: { first: "B", last: "B" } }
]
*/

We only want the people with unique names (so we're using an object as the comparison key)

let result = filterUnique(people, x => x.name);
/*
[
	{ birthDate: "2000-01-01", name: { first: "A", last: "A" } },
	{ birthDate: "2000-01-03", name: { first: "B", last: "B" } },
	{ birthDate: "2000-01-03", name: { first: "C", last: "B" } }
]
*/

Or we can make our own composite keys

let result = filterUnique(people, x => {
	return { foo: x.name.last, bar: x.birthDate };
});
/*
[
	{ birthDate: "2000-01-01", name: { first: "A", last: "A" } },
	{ birthDate: "2000-01-02", name: { first: "A", last: "A" } },
	{ birthDate: "2000-01-03", name: { first: "B", last: "B" } }
]
*/

The last example could also be written as:

let result = filterUnique(people, x => [ x.name.last, x.birthDate ]);