6

I have two arrays. In each array I have objects with lots of properties but no methods. I need to see if array 1 is equal with array 2.

One way to do that would be to create a function that pass through each element of an array and compare each property of the object with the object in the similar position in the second array.

The problem is that the arrays are quite big and also each object has lots of properties. I was wandering if there could be another way. In C++ for example I could read memory... but I don't know how to do that in js.

I need to obtain the most optimal way since this is part of a function that is used often.

Improve this question
1

3 Answers 3

Reset to default
4

Unless they are the same array instance, comparing the memory locations won't work in JavaScript (what happens when you do arr1 == arr2).

You would need to explicitly loop.

Some people use JSON.stringify() (watch out for the gotcha explained in the comments by pimvdb) on both arrays and compare the resulting strings to cheat, but serialising to a string and comparing sounds over fully expensive to me. However it works, so if there is no performance problem, go nuts! :)

You could also try toSource().

I would build my own comparative function that compares just enough that satisfies my idea of identical.

Improve this answer
Sign up to request clarification or add additional context in comments.

5 Comments

There is performance problem :). If I compare arr1 == arr2 will always return false since the memory location is different. I need to compare the memory from that location to the end of the array "in memory terms" to put it like that with the second location to the end. P.S. Please excuse my english.
@zozo JavaScript arrays are really objects with some special methods and properties. They are not typically stored sequentially like other languages' implementations of arrays.
You cannot access address the memory directly as you can in C++. JavaScript is just a dumb interface and all you can do is compare the objects somehow. I would use JSON.stringify too. There's also uneval.
Yeah... so basically I can't avoid the 2 loops. This sucks. :|
JSON.stringify seems to depend on the order in which the properties were added. JSON.stringify({a:1,b:2}) === JSON.stringify({b:2,a:1}) yields false, so I really do not recommend it.
1

Converting your arrays to strings and then comparing the strings will have the same average and worst performance: O(n) (linear).

If you loop through your objects properties/arrays and abort on the 1st mismatch your worst performance will still be O(n) but your average performance might significantly improve unless the objects your'e comparing are usually identical. Either way, since this traversal wouldn't include creating any new objects and copying bytes around - even comparing identical composite objects/arrays (worst case) should still be faster than stringifying them.

As this answer suggests you could just use Underscore.js isEqual:

which according to docs: Performs an optimized deep comparison between the two objects, to determine if they should be considered equal

I'm pretty sure it will work for arrays too.

Improve this answer

Comments

0

JQuery has a function called jQuery.param() which serializes objects

You can compare objects or arrays of objects like so,

$.param( originalObj ) == $.param( modifiedObj )

It's very powerful in conjuction with jQuery.extend() which can be used to clone objects

Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.