Compare two array of objects and return true if they are match

Question

Let's say I have two array of objects as,

let detail1 = [
    {'book':'LOTR','price':'14'}
    {'book':'Harry pottar','price':'12'},      
]

let detail2 = [
    {'book':'Harry pottar','price':'15'},
    {'book':'LOTR','Price':'14'},
    {'book':'HPP','Price':'21'}
]

I want to compare two array of objects and return true or false depending on whether they are same or not.

Note: object's structure i.e. key will always be same, their value may or may not change.

For this I tried as,

for(let i = 0 ;i<detail1.length; i++){
    for(let j = 0; j<detail2.length; j++){
        if(JSON.stringify(detail1[i]) === JSON.stringify(detail2[i])){
            boolValue = true
        } else {
            boolValue = false
        }
    }
}

But this is giving incorrect value for let's say I have another array of object as,

let detail1 = [
    {'book':'LOTR','price':'14'}
    {'book':'Harry pottar','price':'12'},      
]

let detail2 = [
    {'book':'Harry pottar','price':'12'},
    {'book':'LOTR','price':'14'}
]

But when order is changed it's giving incorrect value.

What is the possible solution to compare two array of object and return true if they are same and false if different for any cases given the structure of object i.e. key is same.

Because you are using `stringify` version to compare. You have to compare each and every property. — DecPK, Oct 22 '21 at 10:21
Does this answer your question? [Comparing Arrays of Objects in JavaScript](https://stackoverflow.com/questions/27030/comparing-arrays-of-objects-in-javascript) — pilchard, Oct 22 '21 at 10:55

Alberto Sinigaglia · Accepted Answer · 2021-10-22T10:30:18.210

You can't use JSON encoding for checking the equality, because it's order dependent, eg.:

console.log(
  JSON.stringify({'book':'LOTR','price':'14'}) == JSON.stringify({'price':'14', 'book':'LOTR'})
)

However you can do something like this:

let detail1 = [
    {'book':'LOTR','price':'14'},
    {'book':'Harry pottar','price':'12'},      
]

let detail2 = [
    {'book':'Harry pottar','price':'15'},
    {'book':'LOTR','Price':'14'},
    {'book':'HPP','Price':'21'}
]

function equal(a, b){
  return a.length == b.length && // same length and
         a.every( // every element in a
            e1 => b.some( // has a match in b
               e2 => e1.book == e2.book && e1.price == e2.price
            )
         )
}
console.log(equal(detail1,detail2), equal(detail1,detail1), equal(detail2,detail2))

As @T.J Crowder pointed out, you can actually avoid checking every entry of your object manually and just use Object.entries (be aware of using this only if your objects are composed by only key pair strings)

let detail1 = [
    {'book':'LOTR','price':'14'},
    {'book':'Harry pottar','price':'12'},      
]

let detail2 = [
    {'book':'Harry pottar','price':'15'},
    {'book':'LOTR','Price':'14'},
    {'book':'HPP','Price':'21'}
]

function equal(a, b){
  return a.length == b.length && // same length and
         a.every( // every element in a
            e1 => b.some( // has a match in b
               e2 => Object.keys(e1).every(key => e1[key] === e2[key])
            )
         )
}
console.log(equal(detail1,detail2), equal(detail1,detail1), equal(detail2,detail2))

Well, that's saved me from writing an answer then. :-) Nice one! — T.J. Crowder, Oct 22 '21 at 10:26
@OP - If you wanted to avoid hardcoded property names (e.g., in a utility function), replace `e2 => e1.book == e2.book && e1.price == e2.price` with `Object.keys(e1).every(key => e1[key] === e2[key])`. But if this is just for these specific objects, I'd stick with the names as Alberto showed. — T.J. Crowder, Oct 22 '21 at 10:27
@T.J.Crowder ahah thanks man, yeah you are totally right, I'll add it immediately — Alberto Sinigaglia, Oct 22 '21 at 10:27

score 1 · Answer 2 · answered Oct 22 '21 at 10:36

You can easily achieve the result using Object.keys and every

arr1.length !== arr2.length &&
    arr1.every((o, i) =>
      Object.keys(o).every((prop) => arr2[i][prop] && arr2[i][prop] === o[prop])
    )

let detail1 = [
  { book: "LOTR", price: "14" },
  { book: "Harry pottar", price: "12" },
];

let detail2 = [
  { book: "Harry pottar", price: "15" },
  { book: "LOTR", Price: "14" },
  { book: "HPP", Price: "21" },
];

function isEqual(arr1, arr2) {
  if (arr1.length !== arr2.length) return false;
  return arr1.every((o, i) => {
    return Object.keys(o).every((prop) => {
      return arr2[i][prop] && arr2[i][prop] === o[prop];
    });
  });
}

console.log(isEqual(detail1, detail2));

Compare two array of objects and return true if they are match

2 Answers2