Concatenate array of object inside array of object

Question

Suppose I have array of object as:

const bookDetails = [
    {
        "bookId": "1235",
        "emailId": "samplek@gmail.com",
        "bookIssue": [{"Book not properly aligned": true, "some issue1": true}]
    },
    {
        "bookId": "1235",
        "emailId": "s@gmampleail.com",
        "bookIssue": [{"some issues with book": true, "some issue2": true}]
    }]

I want the O/P as:

[
    {"bookId": "1235", "emailId": "samplek@gmail.com", "bookIssue": "Book not properly aligned,some issue1"},
    {"bookId": "1235", "emailId": "s@gmampleail.com", "bookIssue": "some issues with book,some issue2"}
]

For this I tried,

bookDetails.map((i) => i.bookIssue = Object.keys(i.bookIssue[0]).join(","))

It gives the O/p as required but it starts giving value as,

[{"bookId":"1235","emailId":"samplek@gmail.com","bookIssue":"0"},
{"bookId":"1235","emailId":"s@gmampleail.com","bookIssue":"0"}]

What could be the issue, is there any other way to achieve this?

Yes, it only has one entry, if you are talking about bookIssues — Siva Pradhan, Apr 05 '21 at 10:39
Thank you @georg, I didn't read past the lack of markdown correctly. — T.J. Crowder, Apr 05 '21 at 10:43
@SivaPradhan - Your code works just fine (as georg said) assuming you really want to modify the existing objects you have, although you should use `forEach`, not `map`, because you're not using the array `map` returns. (Or use `for-of` or [any of the other ways of looping arrays](https://stackoverflow.com/questions/9329446/for-each-over-an-array-in-javascript).) — T.J. Crowder, Apr 05 '21 at 10:44

T.J. Crowder · Accepted Answer · 2021-04-05T10:47:20.153

See my comment and georg's, your code works just fine (other than using map incorrectly) provided you want to modify the objects in place.

If you want to create new objects in a new array (e.g., using map correctly), you'd do what you're doing to get the keys but create a new object with the result, like this:

const result = bookDetails.map(entry => {
    // Grab the keys from the first entry and join them
    const bookIssue = Object.keys(entry.bookIssue[0]).join(",");
    // Build the new object to return
    return {...entry, bookIssue};
});

Live Example:

const bookDetails = [
    {"bookId":"1235","emailId":"samplek@gmail.com","bookIssue":[{"Book not properly aligned": true,"some issue1":true}]},
    {"bookId":"1235","emailId":"s@gmampleail.com","bookIssue":[{"some issues with book": true, "some issue2":true }]}
];

const result = bookDetails.map(entry => {
    // Grab the keys from the first entry and join them
    const bookIssue = Object.keys(entry.bookIssue[0]).join(",");
    // Build the return object
    return {...entry, bookIssue};
});

console.log(result);

If bookIssue could have more than one entry (why is it an array if it can't?) and you wanted all of the entries in bookIssue joined together, you could use map on bookIssue getting all of the keys from its objects and joining them, then join the resulting array:

const result = bookDetails.map(entry => {
    const bookIssue = entry.bookIssue
        .map(entry => Object.keys(entry).join(","))
        .join(",");
    // Build the return object
    return {...entry, bookIssue};
});

Live Example:

const bookDetails = [
    {"bookId":"1235","emailId":"samplek@gmail.com","bookIssue":[
        {"Book not properly aligned": true,"some issue1":true},
        {"another issue": true,"yet another issue":true}
    ]},
    {"bookId":"1235","emailId":"s@gmampleail.com","bookIssue":[{"some issues with book": true, "some issue2":true }]}
];

const result = bookDetails.map(entry => {
    const bookIssue = entry.bookIssue
        .map(entry => Object.keys(entry).join(","))
        .join(",");
    // Build the return object
    return {...entry, bookIssue};
});

console.log(result);

That also works if there's just one entry, of course.

Thanks for pointing out ....also I needed to store the value in new variable ...so your solution worked for me... — Siva Pradhan, Apr 05 '21 at 11:50

score 1 · Answer 2 · answered Apr 05 '21 at 10:53

Your code works too, because you're changing the objects bookIssue (same reference as in bookDetails). Here's another way of mapping the attribute bookIssue to the value you want by returning the new object in the map.

const bookDetails = [
    {
        "bookId": "1235",
        "emailId": "samplek@gmail.com",
        "bookIssue": [{"Book not properly aligned": true, "some issue1": true}]
    },
    {
        "bookId": "1235",
        "emailId": "s@gmampleail.com",
        "bookIssue": [{"some issues with book": true, "some issue2": true}]
    }];
    
const output = bookDetails.map(book => {
  return {...book, bookIssue: Object.keys(book.bookIssue[0]).join(',')}
});

console.log(output);

score 1 · Answer 3 · answered Apr 05 '21 at 11:03

Just update your Map function with forEach and see console.log(bookDetails). You were checking map output and not checking bookDetails. That's why you were confused. also in your code check console.log(bookDetails). it will work as expected bookDetails.forEach((i) => i.bookIssue = Object.keys(i.bookIssue[0]).join(","));

Concatenate array of object inside array of object

3 Answers3