Algorithm used to generate a number of recommendations based on selected movies (used in my movie-recs project).

genRecommendation.ts

/**
 * @summary Generates recommendations based on selected items and custom criteria using a point-based system.
 * @param allItems - An array of all available items.
 * @param selectedItems - An array of selected items.
 * @param criteria - An array of functions to calculate points based on different criteria.
 * @param numberOfRecommendations - The number of recommendations to generate, defaults to 3.
 * @returns An array of recommended items.
 * @example
 * const allItems = [1, 2, 3, 4, 5];
 * const selectedItems = [1, 2];
 * const criteria = [
 *  (item, selectedItems) => (selectedItems.includes(item) ? -1 : 1),
 * (item) => (item % 2 === 0 ? 1 : 0),
 * ];
 * const recommendations = genRecommendations(allItems, selectedItems, criteria);
 * console.log(recommendations); // [3, 5, 4]
 */
export const genRecommendations = <T>(
  allItems: T[],
  selectedItems: T[],
  criteria: Array<(item: T, selectedItems: T[]) => number>,
  numberOfRecommendations: number = 3
): T[] => {
  const recommendations = new Map<T, number>();

  allItems.forEach((item) => {
    if (selectedItems.includes(item)) return;

    let points = 0;

    criteria.forEach((criterion) => {
      points += criterion(item, selectedItems);
    });

    recommendations.set(item, points);
  });

  const filteredRecommendations = Array.from(recommendations.entries())
    .sort((a, b) => b[1] - a[1])
    .slice(0, numberOfRecommendations)
    .map(([item]) => item);

  return filteredRecommendations;
};