distinct and distinctBy for streams

[scarf005]

currently it's not very ergonomic to get unique values out of stream. it'd useful to be able to have distinct and distinctBy for Stream.

as-is

import { HashSet } from "https://deno.land/x/rimbu@1.2.0/hashed/mod.ts"
import { Reducer, Stream } from "https://deno.land/x/rimbu@1.2.0/stream/mod.ts"

const distinct = Stream.from(
	Stream.of(1, 2, 1, 2, 3, 2, 3).reduce(Reducer.toJSSet()),
)
console.log(distinct.toArray())
//=> [ 1, 2, 3 ]

const distinctBy = Stream.of({ id: 1 }, { id: 1 }, { id: 2 }, { id: 3 }, { id: 2 })
.reduce(
	HashSet
		.createContext<{ id: number }>({ eq: (a, b) => a.id === b.id })
		.reducer(),
)
	.stream()

console.log(distinctBy.toArray())
//=> [ { id: 3 }, { id: 2 }, { id: 1 } ]

to-be

import { Stream } from "https://deno.land/x/rimbu/stream/mod.ts"

const distinct = Stream.of(1, 2, 1, 2, 3, 2, 3).distinct()
console.log(distinct.toArray())
//=> [ 1, 2, 3 ]

const distinctBy = Stream.of({ id: 1 }, { id: 1 }, { id: 2 }, { id: 3 }, { id: 2 })
.distinctBy((a, b) => a.id === b.id))

console.log(distinctBy.toArray())
//=> [ { id: 3 }, { id: 2 }, { id: 1 } ]

Additional Notes

I'm willing to open a PR.

[vitoke]

Sounds useful indeed. You're welcome to create a PR. I would suggest to create a Transformer that performs this functionality, and then use it in the Stream and AsyncStream implementations, similar to window and distinctPrevious.