sampleSize.js

import copyArray from './.internal/copyArray.js'
import slice from './slice.js'

/**
 * Gets `n` random elements at unique keys from `array` up to the
 * size of `array`.
 *
 * @since 4.0.0
 * @category Array
 * @param {Array} array The array to sample.
 * @param {number} [n=1] The number of elements to sample.
 * @returns {Array} Returns the random elements.
 * @example
 *
 * sampleSize([1, 2, 3], 2)
 * // => [3, 1]
 *
 * sampleSize([1, 2, 3], 4)
 * // => [2, 3, 1]
 */
function sampleSize(array, n) {
  n = n == null ? 1 : n
  const length = array == null ? 0 : array.length
  if (!length || n < 1) {
    return []
  }
  n = n > length ? length : n
  let index = -1
  const lastIndex = length - 1
  const result = copyArray(array)
  while (++index < n) {
    const rand = index + Math.floor(Math.random() * (lastIndex - index + 1))
    const value = result[rand]
    result[rand] = result[index]
    result[index] = value
  }
  return slice(result, 0, n)
}

export default sampleSize