How to group one JSON property based on one other property that appears at many places?

Question

I have this JSON:

var books = [

    { author: "George Owell", title: "1984", price: 0, page: 328}, 
    { author: "Jane Austen", title: "Pride And Prejudice", price: 20, page: 279}, 
    { author: "J.K. Rowling", title: "Harry Potter and the Sorcerer's Stone", price: 23, page: 320}, 
    { author: "Plato", title: "Apology", price: 0, page: 127}, 
    { author: "Sigmund Freud", title: "The Interpretation of Dreams"},
    { author: "George Owell", title: "Animal Farm", price: 0, page: 100}, 
    { author: "George Owell", title: "Omh", price: 0, page: 100}, 
    { author: "Plato", title: "Aristotle", price: 0, page: 227}

];

Now I want to make a table that outputs author and title. If the author is the same, title will be merged together. For example, "George Owell" will have title "1984, Animal Farm, Ohm.", "Plato" will have "Apology, Aristotle", and so on. How can I do it with jQuery or vanilla JavaScript?

There's no JSON in your question: you have an array of objects. Anyway, I would probably use the array `.reduce()` method for this. Are you asking about how to produce HTML output to display the results, or just about how to merge the titles? The merging part can be done (more or less) the same way as in this question: http://stackoverflow.com/questions/33850412/merge-javascript-objects-in-array-with-same-key — nnnnnn, May 18 '17 at 03:32
I can write the code really quickly to do this, if you don't care about the "price" or the "page" - these are "books" so want to create a new object called "authors" then I guess it would make sense... but I am thinking that you might be trying to solve another problem the wrong way. — Tim, May 18 '17 at 03:42

score 1 · Answer 1 · answered May 18 '17 at 04:08

var books = [
    { author: "George Owell", title: "1984", price: 0, page: 328}, 
    { author: "Jane Austen", title: "Pride And Prejudice", price: 20, page: 279}, 
    { author: "J.K. Rowling", title: "Harry Potter and the Sorcerer's Stone", price: 23, page: 320}, 
    { author: "Plato", title: "Apology", price: 0, page: 127}, 
    { author: "Sigmund Freud", title: "The Interpretation of Dreams"},
    { author: "George Owell", title: "Animal Farm", price: 0, page: 100}, 
    { author: "George Owell", title: "Omh", price: 0, page: 100}, 
    { author: "Plato", title: "Aristotle", price: 0, page: 227}
];

var uniqueauthors = [];
$.each(books,function(index,value){
if($.inArray(value.author,uniqueauthors) < 0)
{
uniqueauthors.push(value.author);
}
});

$.each(uniqueauthors,function(index,value){
var bok = $.map(books,function(val,index){
return (val.author == value) ? val.title : null;
});
var $tr = $('<tr>').append('<td>'+value+'</td>').append('<td>'+bok.join(",")+'</td>');
$('table').append($tr);
});

td{
  border: 1px solid black;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<table>
<tr>
<td>Authors</td>
<td>Titles</td>
</tr>
</table>

score 0 · Answer 2 · answered May 18 '17 at 03:47

Something like the following should get you started:

var books = [

    { author: "George Owell", title: "1984", price: 0, page: 328}, 
    { author: "Jane Austen", title: "Pride And Prejudice", price: 20, page: 279}, 
    { author: "J.K. Rowling", title: "Harry Potter and the Sorcerer's Stone", price: 23, page: 320}, 
    { author: "Plato", title: "Apology", price: 0, page: 127}, 
    { author: "Sigmund Freud", title: "The Interpretation of Dreams"},
    { author: "George Owell", title: "Animal Farm", price: 0, page: 100}, 
    { author: "George Owell", title: "Omh", price: 0, page: 100}, 
    { author: "Plato", title: "Aristotle", price: 0, page: 227}
    ];


   var authorBooks = {}

   books.forEach(function(book) {

      if(!authorBooks[book.author]) {
        authorBooks[book.author] = [];
      }

      authorBooks[book.author].push({title: book.title, price: book.price, page: book.page});

    },{});

score 0 · Answer 3 · edited May 23 '17 at 12:34

Same question popped up yesterday in python. Here's my answer: https://stackoverflow.com/a/44017627/7633845

Here's a js version:

var map = {}
for(var i = 0; i < books.length; i++) {
    var book = books[i];
    if(!(book.author in map)) {
        map[book.author] = []
    }
    map[book.author].push(book.title)
}

var out = []
for(var author in map) {
    out.push({
        author: author,
        books: map[author].join(", ")
    })
}

score 0 · Answer 4 · answered May 18 '17 at 04:02

you can try

var books = [

{ author: "George Owell", title: "1984", price: 0, page: 328}, 
{ author: "Jane Austen", title: "Pride And Prejudice", price: 20, page: 279}, 
{ author: "J.K. Rowling", title: "Harry Potter and the Sorcerer's Stone", price: 23, page: 320}, 
{ author: "Plato", title: "Apology", price: 0, page: 127}, 
{ author: "Sigmund Freud", title: "The Interpretation of Dreams"},
{ author: "George Owell", title: "Animal Farm", price: 0, page: 100}, 
{ author: "George Owell", title: "Omh", price: 0, page: 100}, 
{ author: "Plato", title: "Aristotle", price: 0, page: 227}
];

var results = books.reduce((previous, book) => {
(previous[book.author] = previous[book.author] || []).push(book);
    return previous;
}, []);

console.log(results);

How to group one JSON property based on one other property that appears at many places?

4 Answers4