Line data    Source code

       1             : import { Engine } from "../types.ts";
       2           1 : import { sliceArray } from "../utils/sliceArray.ts";
       3           1 : import { shuffle } from "./shuffle.ts";
       4             : 
       5             : /**
       6             :  * From the population array, produce an array with sampleSize elements that
       7             :  * are randomly chosen without repeats.
       8             :  * @param engine The Engine to use when choosing random values
       9             :  * @param population An array that has items to choose a sample from
      10             :  * @param sampleSize The size of the result array
      11             :  */
      12           0 : export function sample<T>(
      13           0 :   engine: Engine,
      14           0 :   population: ArrayLike<T>,
      15           0 :   sampleSize: number
      16             : ): T[] {
      17           0 :   if (
      18           0 :     sampleSize < 0 ||
      19           0 :     sampleSize > population.length ||
      20           0 :     !isFinite(sampleSize)
      21           0 :   ) {
      22           0 :     throw new RangeError(
      23           0 :       "Expected sampleSize to be within 0 and the length of the population"
      24           0 :     );
      25           0 :   }
      26             : 
      27           0 :   if (sampleSize === 0) {
      28           0 :     return [];
      29           0 :   }
      30             : 
      31           0 :   const clone = sliceArray.call(population);
      32           0 :   const length = clone.length;
      33           0 :   if (length === sampleSize) {
      34           0 :     return shuffle(engine, clone, 0);
      35           0 :   }
      36           0 :   const tailLength = length - sampleSize;
      37           0 :   return shuffle(engine, clone, tailLength - 1).slice(tailLength);
      38           0 : }