Javascript merging an array with array objects

Question

var authors = [
 {authorIndex:1, author:"John Steinbeck"},
 {authorIndex:2, author:"Franz Kafka"},
 {authorIndex:3, author:"J. R. R. Tolkien"},
 {authorIndex:4, author:"Charles Dickens"}];
var books = [
 {title:"The Grapes of Wrath",authorIndex:4,pubYear:1936},
 {title:"The Hobbit",authorIndex:2,pubYear:1937},
 {title:"The Trial",authorIndex:1,pubYear:1937},
 {title:"A Tale of Two Cities",authorIndex:3,pubYear:1859}];

What I want to do is insert authors in books and to be connected with authorsIndex

• Nina Scholz: please add the result and the code, you tried. --> minimal reproducible example

Answer 1

Considering your authors array will have unique authorIndex values, first create an object having authorIndex as keys and relevant object as its value. Then iterate over your books array and merge object properties using Object.assign():

var authors = [
 {authorIndex:1, author:"John Steinbeck"}, {authorIndex:2, author:"Franz Kafka"},
 {authorIndex:3, author:"J. R. R. Tolkien"}, {authorIndex:4, author:"Charles Dickens"}
];
var books = [
 {title:"The Grapes of Wrath",authorIndex:4,pubYear:1936},
 {title:"The Hobbit",authorIndex:2,pubYear:1937},
 {title:"The Trial",authorIndex:1,pubYear:1937},
 {title:"A Tale of Two Cities",authorIndex:3,pubYear:1859}
];
 
var authorsObj = authors.reduce((r, c) => (r[c.authorIndex] = c, r), {});
var result = books.map(o => Object.assign(o, authorsObj[o.authorIndex]));
console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 2

 const result = authors.map(val => {
 return Object.assign({}, val, books.filter(v => v.authorIndex === val.authorIndex)[0]);
 console.log(result);
 });
 console.log(result);

This is will give the combined array of both authors and books

Answer 3

books.forEach(function(value,index){
 var ind = value.authorIndex;
 var matchAuthor = authors.find(function(element){
 return element.authorIndex == ind;
 });
 value.author = matchAuthor.author;
})

There are a lot of solutions one of them is this, Please check the link

Answer 4

Here is another concise option using lodash for those who are interested:

var authors = [{ authorIndex: 1, author: "John Steinbeck" }, { authorIndex: 2, author: "Franz Kafka" }, { authorIndex: 3, author: "J. R. R. Tolkien" }, { authorIndex: 4, author: "Charles Dickens" } ];
var books = [{ title: "The Grapes of Wrath", authorIndex: 4, pubYear: 1936 }, { title: "The Hobbit", authorIndex: 2, pubYear: 1937 }, { title: "The Trial", authorIndex: 1, pubYear: 1937 }, { title: "A Tale of Two Cities", authorIndex: 3, pubYear: 1859 } ];
const aMap = _.keyBy(authors, 'authorIndex')
const result = _.map(books, x => _.merge(x, aMap[x.authorIndex]))
console.log(result)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

We do keyBy to make sure we have a key map for reference and them we map and for each item we do merge.