Add toSet feature (#34)

* add `toSet` feature

* update changelog

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `includes` feature ([#24](https://github.com/RobinMalfait/lazy-collections/pull/24), [#29](https://github.com/RobinMalfait/lazy-collections/pull/29))
 - Add `at` feature ([#25](https://github.com/RobinMalfait/lazy-collections/pull/25), [#30](https://github.com/RobinMalfait/lazy-collections/pull/30))
 - Add `product` feature ([#33](https://github.com/RobinMalfait/lazy-collections/pull/33))
+- Add `toSet` feature ([#34](https://github.com/RobinMalfait/lazy-collections/pull/34))
 
 ### Fixed
 

README.md

@@ -86,6 +86,7 @@ program(range(0, 1000000))
     - [`takeWhile`](#takewhile)
     - [`tap`](#tap)
     - [`toArray`](#toarray)
+    - [`toSet`](#toset)
     - [`unique`](#unique)
     - [`wait`](#wait)
     - [`where`](#where)
@@ -865,6 +866,21 @@ program()
 // [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ]
 ```
 
+#### `toSet`
+
+[Table of contents](#table-of-contents)
+
+Converts an array or an iterator to Set.
+
+```js
+import { pipe, range, toSet } from 'lazy-collections'
+
+let program = pipe(range(0, 10), toSet())
+
+program()
+// Set (11) { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }
+```
+
 #### `unique`
 
 [Table of contents](#table-of-contents)

src/__snapshots__/index.test.ts.snap

@@ -41,6 +41,7 @@ exports[`should export all the things 1`] = `
   "takeWhile": [Function],
   "tap": [Function],
   "toArray": [Function],
+  "toSet": [Function],
   "unique": [Function],
   "wait": [Function],
   "where": [Function],

src/index.ts

@@ -40,6 +40,7 @@ export * from './take'
 export * from './takeWhile'
 export * from './tap'
 export * from './toArray'
+export * from './toSet'
 export * from './unique'
 export * from './where'
 export * from './windows'

src/toSet.test.ts

@@ -0,0 +1,29 @@
+import { pipe, range, flatMap, toSet, delay } from './'
+
+it('should convert an iterator to an array', () => {
+  let program = pipe(range(0, 10), toSet())
+
+  expect(program()).toEqual(new Set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))
+})
+
+it('should remove duplicate items (default Set behaviour)', () => {
+  let program = pipe(
+    range(0, 10),
+    flatMap<number, number[]>((value) => [value, value, value + 1]),
+    toSet()
+  )
+
+  expect(program()).toEqual(new Set([0, 1, 10, 11, 2, 3, 4, 5, 6, 7, 8, 9]))
+})
+
+it('should convert an iterator to an array (async)', async () => {
+  let program = pipe(range(0, 10), delay(0), toSet())
+
+  expect(await program()).toEqual(new Set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))
+})
+
+it('should convert an iterator to an array (Promise async)', async () => {
+  let program = pipe(Promise.resolve(range(0, 10)), toSet())
+
+  expect(await program()).toEqual(new Set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]))
+})

src/toSet.ts

@@ -0,0 +1,12 @@
+import { reduce } from './'
+
+import { LazyIterable } from './shared-types'
+
+export function toSet<T>() {
+  return (data: LazyIterable<T>) => {
+    return reduce<Set<T>, T>((acc, current) => {
+      acc.add(current)
+      return acc
+    }, new Set<T>())(data)
+  }
+}