How to filter an object array based on the contents of child array?

Question

I have this data

var data = [
  {
    title: "App development summary",
    category: [],
  },
  {
    title: "to experiment 2",
    category: [],
  },
  {
    title: "Some of these books I have read",
    category: [
      {
        _id: "5f7c99faab20d14196f2062e",
        name: "books",
      },
      {
        _id: "5f7c99faab20d14196f2062f",
        name: "to read",
      },
    ],
  },
  {
    title: "Quora users and snippets",
    category: [
      {
        _id: "5f7c99feab20d14196f20631",
        name: "quora",
      },
    ],
  },
  {
    title: "Politics to research",
    category: [
      {
        _id: "5f7c9a02ab20d14196f20633",
        name: "politics",
      },
    ],
  },
];

Say I want to get all the entries with the category of books. I tried doing this:

var bookCat = data.map(note => {
 return note.category.map(cat => {
   if(cat.name === "books" ) return note
 })
})

But the result comes back with some empty and undefined arrays.

I was able to filter the empty arrays (at one point) but not the undefined

Edit

In plain English "if the object ha category.name "books", give me the title"

@CertainPerformance yes, that's part of the categories. I'm trying to get the book that has the category of 'book' the fact that it also has the category 'to read' doesn't matter. — relidon
– relidon, Commented Oct 11, 2020 at 21:57
@Phil the result from the above would be data[2] that's the only object with the category of book. I misread the answer given. the code actually works but doesn't loop. If there was another object like data[2] the code provided in the first answer would not show it. this jsbin.com/popibedugu/edit?js,console selects the right one but leaves out the other — relidon
– relidon, Commented Oct 11, 2020 at 22:57

CertainPerformance · Accepted Answer · 2020-10-11 22:41:20Z

2

Filter by whether the array's category contains at least one name which is books:

var data=[{title:"App development summary",category:[]},{title:"to experiment 2",category:[]},{title:"Some of these books I have read",category:[{_id:"5f7c99faab20d14196f2062e",name:"books"},{_id:"5f7c99faab20d14196f2062f",name:"to read"}]},{title:"Quora users and snippets",category:[{_id:"5f7c99feab20d14196f20631",name:"quora"}]},{title:"Politics to research",category:[{_id:"5f7c9a02ab20d14196f20633",name:"politics"}]}];

const output = data
  .filter(item => item.category.some(
    ({ name }) => name === 'books'
  ));
console.log(output);

If there's guaranteed to be only a single matching object, use .find instead:

var data=[{title:"App development summary",category:[]},{title:"to experiment 2",category:[]},{title:"Some of these books I have read",category:[{_id:"5f7c99faab20d14196f2062e",name:"books"},{_id:"5f7c99faab20d14196f2062f",name:"to read"}]},{title:"Quora users and snippets",category:[{_id:"5f7c99feab20d14196f20631",name:"quora"}]},{title:"Politics to research",category:[{_id:"5f7c9a02ab20d14196f20633",name:"politics"}]}];

const output = data
  .find(item => item.category.some(
    ({ name }) => name === 'books'
  ));
console.log(output);

edited Oct 11, 2020 at 22:41

answered Oct 11, 2020 at 21:57

CertainPerformance

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4 Comments

relidon Over a year ago

That's not what I want. I want the entire parent of the category

relidon Over a year ago

In plain English "if the object ha category.name "books", give me the title". That's what I'm having trouble with, getting the parent array the moment I've filtered the category name.

relidon Over a year ago

Sorry again, what if there are two objects with the category 'books'. jsbin.com/popibedugu/edit?js,console I added another entry and doesn't show

CertainPerformance Over a year ago

@relidon It looks to work? It shows a result array of length 2 - both objects with a books get included

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