Artigos | Array.reduce  - O canivete suíço da programação funcional | Array multidimensional

reduce-array-multidimensional.js

const users = [
  {
    name: 'User #1',
    bookmarks: [
      { title: 'Movie #1', id: 1 },
      { title: 'Movie #6', id: 6 },
      { title: 'Movie #3', id: 3 },
    ]
  },
  {
    name: 'User #2',
    bookmarks: [
      { title: 'Movie #1', id: 1 },
      { title: 'Movie #4', id: 4 },
      { title: 'Movie #6', id: 6 },
      { title: 'Movie #2', id: 2 },
    ]
  }
];

const bookmarks = users
  .map(user => user.bookmarks)              /* from: [ { #: [{...}] }, { #: [{...}] } ] */
  .reduce((bookmarks, movies) => {          /* to:   [ [{...}], [{...}] ]               */
    return bookmarks
      .concat(movies.filter((movie) => {
        return bookmarks
          .map(movie => movie.id)
          .indexOf(movie.id) === -1;
      }));
  }, []);                                   /* from: [ [{...}], [{...}] ] */
                                            /* to:   [ {...}, {...} ]     */

/*
  #bookmarks
  
  [
    { title: 'Movie #1', id: 1 },
    { title: 'Movie #6', id: 6 },
    { title: 'Movie #3', id: 3 },
    { title: 'Movie #4', id: 4 },
    { title: 'Movie #2', id: 2 },
  ]
*/