sync

src/random/index.ts

@@ -1,6 +1,6 @@
 import { BitArray } from "../bitarray/index.js";
 import { asArray } from "../utils.js";
-import { AsyncRandomOptions, ElementPredicate, ElementWeight, RandomGenerator, RandomOptions } from "./types.js";
+import { AsyncRandomOptions, ElementPredicate, ElementWeight, RandomElement, RandomGenerator, RandomOptions } from "./types.js";
 
 export const alwaysTrue: ElementPredicate = () => true;
 export const weightOfOne: ElementWeight = () => 1.0;
@@ -45,9 +45,10 @@ function withDefaultOptions<T>(options: RandomOptions<T> | AsyncRandomOptions<T>
   };
 }
 
-function _getRandomElement<T>(sequence: Iterable<T>, options: Required<RandomOptions<T>>) {
+function _getRandomElement<T>(sequence: Iterable<T>, options: Required<RandomOptions<T>>): RandomElement<T> {
   const { predicate, weight, random } = options;
 
+  let found = false;
   let result: T | undefined = undefined;
   let resultIndex = -1;
   let index = 0;
@@ -66,22 +67,24 @@ function _getRandomElement<T>(sequence: Iterable<T>, options: Required<RandomOpt
       weightAcc += w;
 
       if (random() * weightAcc < w) {
+        found = true;
         result = element;
         resultIndex = currentIndex;
       }
     }
   }
 
-  return { element: result, index: resultIndex };
+  return { found, element: result, index: resultIndex } as RandomElement<T>;
 }
 
 export function getRandomElement<T>(sequence: Iterable<T>, options?: RandomOptions<T>) {
   return _getRandomElement(sequence, withDefaultOptions(options));
 }
 
-async function _getRandomElementAsync<T>(sequence: AsyncIterable<T>, options: Required<AsyncRandomOptions<T>>) {
+async function _getRandomElementAsync<T>(sequence: AsyncIterable<T>, options: Required<AsyncRandomOptions<T>>): Promise<RandomElement<T>> {
   const { predicate, weight, random } = options;
 
+  let found = false;
   let result: T | undefined = undefined;
   let resultIndex = -1;
   let index = 0;
@@ -100,13 +103,14 @@ async function _getRandomElementAsync<T>(sequence: AsyncIterable<T>, options: Re
       weightAcc += w;
 
       if (random() * weightAcc < w) {
+        found = true;
         result = element;
         resultIndex = currentIndex;
       }
     }
   }
 
-  return { element: result, index: resultIndex };
+  return { found, element: result, index: resultIndex } as RandomElement<T>;
 }
 
 export async function getRandomElementAsync<T>(sequence: AsyncIterable<T>, options?: AsyncRandomOptions<T>) {

src/random/types.ts

@@ -4,7 +4,7 @@ export type ElementPredicate<T = any> = (index: number, obj: T) => boolean;
 export type ElementWeight<T = any> = (index: number, obj: T) => number;
 export type RandomGenerator = () => number;
 
-export interface RandomOptions<T = any> {
+export type RandomOptions<T = any> = {
   predicate?: ElementPredicate<T>;
   weight?: ElementWeight<T>;
   random?: RandomGenerator;
@@ -13,8 +13,20 @@ export interface RandomOptions<T = any> {
 export type MaybeAsyncElementPredicate<T = any> = MaybeAsyncFunction<ElementPredicate<T>>;
 export type MaybeAsyncElementWeight<T = any> = MaybeAsyncFunction<ElementWeight<T>>;
 
-export interface AsyncRandomOptions<T = any> {
+export type AsyncRandomOptions<T = any> = {
   predicate?: MaybeAsyncElementPredicate<T>;
   weight?: MaybeAsyncElementWeight<T>;
   random?: RandomGenerator;
 };
+
+type RandomElementFound<T> = {
+  found: true;
+  element: T;
+  index: number;
+};
+type RandomElementNotFound = {
+  found: false;
+  element: undefined;
+  index: -1;
+};
+export type RandomElement<T> = RandomElementFound<T> | RandomElementNotFound;