Filter inside a nested array with objects

Question

I have an array that contains three book objects. Each book object has an array of bookIds . I want to filter by bookId (3,1) in a fast and efficient way since my array will grow up easly in the future. I tried with map, but it change my original array even with a deepCopy ! Is there a way to use the filter function instead without using recursivity ?

this.booksList = 
    [
      {
        "books": [
          {
            "bookId": 3
          },
          {
            "bookId": 2
          }
        ],
        "id": 1,
        "name": "Name 1",
        "description": "desc 1"
      },
      {
        "books": [
          {
            "bookId": 5
          },
          {
            "bookId": 2
          }
         ],
         "id": 2,
         "name": "Name 2",
         "description": "desc 2"
      },
      {
        "books": [
          {
            "bookId": 1
          },
          {
            "bookId": 3
          }
         ],
         "id": 3,
         "name": "Name 3",
         "description": "desc 3"
      }
    ]

The map approach :

let results = this.books.map(function (book) {
            book.books = book.books.filter(x => x.bookId == 1 || x.bookId == 3);
            return book;
        }).filter(({ books }) => books.length);

Result with map : not expected result !

[
  {
    "books": [
      {
        "bookId": 3
      }
    ],
    "id": 1,
    "name": "Name 1",
    "description": "desc 1"
  },
  {
    "books": [
      {
        "bookId": 1
      },
      {
        "bookId": 3
      }
     ],
     "id": 3,
     "name": "Name 3",
     "description": "desc 3"
  }
]

expected results :

[
  {
    "books": [
      {
        "bookId": 3
      },
      {
        "bookId": 2
      }
    ],
    "id": 1,
    "name": "Name 1",
    "description": "desc 1"
  },
  {
    "books": [
      {
        "bookId": 1
      },
      {
        "bookId": 3
      }
     ],
     "id": 3,
     "name": "Name 3",
     "description": "desc 3"
  }
]

Thanks,

yes it does ! otherwise i will keep the map solution. See my post that i just updated — Kivo
– Kivo, Commented Sep 19, 2020 at 23:28
You passed a function that changes books as the callback to map. map just calls you callback and returns its result. — Aluan Haddad
– Aluan Haddad, Commented Sep 19, 2020 at 23:29
Try const results = books.map(x => ({...x, books: x.books.filter(b => b.bookId === 1 || b.bookId === 3)})) — Aluan Haddad
– Aluan Haddad, Commented Sep 19, 2020 at 23:32
i have the same results as the not expected result in my post but with your version my original array didn't change this time, so that's a good start :) — Kivo
– Kivo, Commented Sep 19, 2020 at 23:45

Mulan · Accepted Answer · 2020-09-19 23:43:52Z

2

I think you are looking for filter and some -

const input =
  [{books:[{bookId:3},{bookId:2}],id:1,name:"Name 1",description:"desc 1"},{books:[{bookId:5},{bookId:2}],id:2,name:"Name 2",description:"desc 2"},{books:[{bookId:1},{bookId:3}],id:3,name:"Name 3",description:"desc 3"}]

const query =
  [3, 1]

const result =
  input.filter(({ books = [] }) =>
    books.some(({ bookId = null }) => query.includes(bookId))
  )

console.log(JSON.stringify(result, null, 2))

Output -

[
  {
    "books": [
      {
        "bookId": 3
      },
      {
        "bookId": 2
      }
    ],
    "id": 1,
    "name": "Name 1",
    "description": "desc 1"
  },
  {
    "books": [
      {
        "bookId": 1
      },
      {
        "bookId": 3
      }
    ],
    "id": 3,
    "name": "Name 3",
    "description": "desc 3"
  }
]

answered Sep 19, 2020 at 23:43

Mulan

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Comments

Roko C. Buljan · Accepted Answer · 2020-09-19 23:51:32Z

0

const booksList=[
  {books:[{bookId:3},{bookId:2}],id:1,name:"Name 1",description:"desc 1"},
  {books:[{bookId:5},{bookId:2}],id:2,name:"Name 2",description:"desc 2"},
  {books:[{bookId:1},{bookId:3}],id:3,name:"Name 3",description:"desc 3"},
];

const byBookIDs = (...IDs) =>
  booksList.filter(b => b.books.some(b => IDs.includes(b.bookId)));

console.log(byBookIDs(1, 3));

MDN Array Filter - to return a subset
MDN Array Some - to match (and return) as soon as some
MDN Array Includes - to find item in array

edited Sep 19, 2020 at 23:51

answered Sep 19, 2020 at 23:46

Roko C. Buljan

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Filter inside a nested array with objects

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