Create new array based on comparison between two array of objects

Question

Suppose I have two array of Object as,

let oldBookDetails = [
    {'name':'Harry pottar','amount':10, is_modified: false},
    {'name':'LOTR','amount':20, is_modified: false},
    {'name':'dune','amount':15, is_modified: false}
]

let newBookDetails = [
    {'name':'Harry pottar','amount':15},
    {'name':'LOTR','amount':20},
    {'name':'HR','amount':15}
]

let bookModified = []

I want to create new array of Object by comparing newBookDetails with oldBookDetails,

and check if any name is removed newDetails, don't push into the bookModified array,

if amount has been changed then push newBookDetails object into bookModified with is_modified: true and if newBookDetails amount is same push into bookModified array with is_modified:false.

For this I tried as:

newBookDetails.forEach((el) => {

    oldBookDetails.forEach((ele) => {

        if(Object.values(el).indexOf(el.name) > -1) {
            if(el.amount === ele.amount) {
                bookModified.push(el)
            }else if(el.amount != ele.amount) {
                el.is_modified = true
                bookModified.push(el)
            }
        } else if(Object.values(el).indexOf(el.name) === -1) {
            //this loops as all are not equal....i am stuck from this part.
        }
    })
})

Expected O/P :

console.log(newBookDetails)

[
    {'name':'Harry pottar','amount':15, is_modified: true},
    {'name':'LOTR','amount':20, is_modified: false},
    {'name':'HR','amount':15, is_modified: true}
]

If anyone needs any further information please do let me know.

Object.values(el).indexOf(el.name) > -1 is checking if the current el object has a name propety value that is in el - this will alaways be true, as you're grabbing a value from your object, and then checking if that value is in that same object. You probably want to compare names from both objects: ele.name === el.name. Your else if can also be made into just else (or even removed entirely) — Nick Parsons
– Nick Parsons, Commented Oct 5, 2021 at 8:25

Nitheesh · Accepted Answer · 2021-10-05 09:46:37Z

2

You can do it using map() and find():

map() on the second array and try to find the book in the first one using property name. If not found pass in modified true, else check the amount and pass modified value accordingly.

let oldBookDetails = [
  { 'name': 'Harry pottar', 'amount': 10, is_modified: false },
  { 'name': 'LOTR', 'amount': 20, is_modified: false },
  { 'name': 'dune', 'amount': 15, is_modified: false }
];

let newBookDetails = [
  { 'name': 'Harry pottar', 'amount': 15 },
  { 'name': 'LOTR', 'amount': 20 },
  { 'name': 'HR', 'amount': 15 }
];

let bookModified = newBookDetails.map((x) => {
  let foundBook = oldBookDetails.find(old => old.name === x.name);
  if (foundBook) {
    if (foundBook.amount !== x.amount)
      return { ...x, is_modified: true };
    else
      return { ...x, is_modified: false };
  }
  else
    return { ...x, is_modified: true };
});
console.log(bookModified);

edited Oct 5, 2021 at 9:46

Nitheesh

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answered Oct 5, 2021 at 8:24

Tushar Shahi

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4 Comments

user5734311 Over a year ago

My solution: jsfiddle.net/1zLtu9qc

Tushar Shahi Over a year ago

Edited the answer with ... operator. Missed that part

Sushant Rad Over a year ago

Actually I have one more query should I ask new question or can I update in the same.:: My query::Create a variable string to keep note of whether amount has been reduced or increased or removed and for which book. Ex: 'Owner removed Book dune'

Nitheesh Over a year ago

@SushantRad see my anser for that check. I have incooperated that aswell.

Shravan Kumar · Accepted Answer · 2021-10-05 08:38:14Z

0

You can do with below snippet

newBookDetails.forEach(newBook => {
  let found = false;
  oldBookDetails.forEach(oldBook => {
    if (oldBook.name === newBook.name) {
      if (oldBook.amount === newBook.amount) {
        bookModified.push({
          'name': newBook.name,
          'amount': newBook.amount,
          is_modified: false
        })
      } else {
        bookModified.push({
          'name': newBook.name,
          'amount': newBook.amount,
          is_modified: true
        })
      }
      found = true;
    }
  })
  if (!found) {
    bookModified.push({
      'name': newBook.name,
      'amount': newBook.amount,
      is_modified: true
    })
  }
})

answered Oct 5, 2021 at 8:38

Shravan Kumar

11 bronze badge

1 Comment

user5734311 Over a year ago

Here's a shorter way: jsfiddle.net/1zLtu9qc

Abror Abdullaev · Accepted Answer · 2021-10-05 08:38:38Z

0

let oldBookDetails = [
    {'name':'Harry pottar','amount':10, is_modified: false},
    {'name':'LOTR','amount':20, is_modified: false},
    {'name':'dune','amount':15, is_modified: false}
]

let newBookDetails = [
    {'name':'Harry pottar','amount':15},
    {'name':'LOTR','amount':20},
    {'name':'HR','amount':15}
]

let bookModified = oldBookDetails
  .filter((oldBookDetail) => newBookDetails.findIndex((bookDetails) => bookDetails.name === oldBookDetail.name) > -1)
  .map((oldBookDetails) => {
  const newDetails = newBookDetails.find((bookDetails) => bookDetails.name === oldBookDetails);
  return {...oldBookDetails, ...newDetails};
});

console.log(bookModified);

Could be done better though, if you spend more time in optimizing and sharpening

answered Oct 5, 2021 at 8:38

Abror Abdullaev

2791 silver badge6 bronze badges

1 Comment

user5734311 Over a year ago

Wrong result. Right way: jsfiddle.net/1zLtu9qc

Nitheesh · Accepted Answer · 2021-10-05 13:06:43Z

Array.map will help you to generate the new array as per your requirement.

Logic

Loop through newBookDetails array.
Check if node from newBookDetails is present in oldBookDetails
If no return the newBook node with is_modified as true
If yes. return the node with is_modified value as a boolean that compare the new book and old book price.
To find the removed book, filter the oldBookDetails array and check nodes that are not prtesent in newBookDetails

const oldBookDetails = [ {'name':'Harry pottar','amount':10, is_modified: false}, {'name':'LOTR','amount':20, is_modified: false}, {'name':'dune','amount':15, is_modified: false}];
const newBookDetails = [ {'name':'Harry pottar','amount':15}, {'name':'LOTR','amount':20}, {'name':'HR','amount':15} ];
const bookModified = newBookDetails.map((node) => {
  const oldBookNode = oldBookDetails.find((item) => item.name === node.name);
  if (oldBookNode) {
    return { ...node, is_modified: oldBookNode.amount !==  node.amount }
  } else {
    return { ...node, is_modified: true };
  }
});
const removedBooks = oldBookDetails.filter((book) => !newBookDetails.find((node) => node.name === book.name));
console.log(bookModified);
console.log(removedBooks);

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