filter

filter :: (Collection collection, Function predicate) -> Collection | Promise<Collection>

description

Iterates over a collection (Array, Object, Map, Set) and returns a new collection of the same type containing only the values for which the predicate function evaluates to true.

Like many Collection methods in Conductor, filter works with both asynchronous & synchronous mappers. If you use a synchronous predicate function, filter will work like Array.prototype.filter and return a Collection synchronously.

const values = [0, 1, 2, 3]
const isEven = x => x % 2 === 0
filter(isEven, values) // [0, 2]

If you use an asynchronous mapper, filter will return a Promise, and you will need to use await or Promise.prototype.then to retrieve the new collection.

const values = [0, 1, 2, 3]
const isEven = async x => x % 2 === 0
filter(double, values) // Promise<Pending>
await filter(double, values) // [0, 2]

Important

If you use an asynchronous predicate function, all predicate calls will be done in parallel, but the input collection's order will be preserved.