group array of objects with inner array of strings javascript-CodePudding

I have an array of objects like below -

const books = [
  {
    name:"abc",
    isbn: 123,
    tags: ["tagA","tagB","tagC"]
  },
  {
    name:"xyz",
    isbn: 456,
    tags: ["tagB","tagC"]
  },
  {
    name:"pqr",
    isbn: 456,
    tags: ["tagB"]
  }
];

I want to group it based on tags of each object, and push the matched objects into the tags values which is string array. My expected output shoulb be an object having the grouped value as key and the value should be the array of matched values.

My Expected Output is-

const expected = {
    "tagA" : [
     {
         name:"abc",
       isbn: 123,  
     },
  ],
    "tagB" : [
     {
         name:"abc",
       isbn: 123,  
     },
     {
         name:"xyz",
       isbn: 456,  
     },
     {
         name:"pqr",
       isbn: 456,  
     },
  ],
    "tagC" : [
      {
         name:"abc",
       isbn: 123,  
     },
     {
         name:"xyz",
       isbn: 456,  
     },
  ],
}

CodePudding user response：

There are similar questions for grouping by key; since you want to group based on value of key which is array, you could do something like this:

const books = [
  {
    name:"abc",
    isbn: 123,
    tags: ["tagA","tagB","tagC"]
  },
  {
    name:"xyz",
    isbn: 456,
    tags: ["tagB","tagC"]
  },
  {
    name:"pqr",
    isbn: 456,
    tags: ["tagB"]
  }
];

let grouped = {};

books.forEach((book)=>{

 book.tags.forEach(tag=>{
   if(!grouped[tag]) grouped[tag] = [{name:book.name,isbn:book.isbn}]
   else grouped[tag].push({name:book.name,isbn:book.isbn})
 })

})

console.log(grouped)

CodePudding user response：

This is a very standard 'group by' with an extra loop to add each element to multiple groups.

const books = [{ name: "abc", isbn: 123, tags: ["tagA", "tagB", "tagC"] }, { name: "xyz", isbn: 456, tags: ["tagB", "tagC"] }, { name: "pqr", isbn: 456, tags: ["tagB"] }];

const result = {};
for (const { tags, ...book } of books) {
  for (const tag of tags) {
    (result[tag] ??= []).push({...book});
  }
}

console.log(result);