Efficient way to compare arrays in javascript

Question

I need to compare the elements from two arrays as follows:

arr1[0] ? arr2[0]
arr1[1] ? arr2[1]
arr1[2] ? arr2[2]
etc.

I wrote some code but it seems to be slow when I try to compare 1000 objects like this on each array :

{
 "id":"event707",
 "name":"Custom707",
 "type":"disabled",
 "default_metric":false,
 "participation":"disabled",
 "serialization":"always_record"
}

This is how my function looks like (just an example for two arrays with hard coded data).

function compare() {
 var step = 0;
 var fruits1 = [{"apple":25},{"bannana":36},{"orange":6}];
 var fruits2 = [{"apple":25},{"bannana":36},{"orange":6}];
 for(var i=0;i<fruits1.length;i++) {
 for(var j=step;j<fruits2.length;j++) {
 console.log("FRUIT1");
 console.log(JSON.stringify(fruits1[i]));
 console.log("FRUIT2");
 console.log(JSON.stringify(fruits2[j]));
 console.log("----------------------");
 if(JSON.stringify(fruits1[i])!== JSON.stringify(fruits2[j])) {
 //do something
 }
 step = step + 1;
 break;
 }
 }
}

• Icepickle: The way you show your comparison, you only need one indexer, and then you can use i to compare fruits1[i] with fruits2[i]. I don't really see a reason / necessity for the step variable. So, if you need to compare based on the index as well (eg: fruits1[1] has to be equal with fruits2[1] then I think you need to simplify your algorithm). This way, you could already say that 2 arrays are not the same because of a length difference between both arrays, and if they are, exit the loop as soon as you have a mismatch on the same positions of your array
• Valip: You're right, there is no need for the step variable. I changed my code and now the response time is lower by 1 minute ! Thank you!

Answer 1

With an invention of Object.prototype.compare() and Array.prototype.compare() this job becomes a very simple task. Array compare can handle both primitive and reference type items. Objects are compared shallow. Let's see how it works;

Object.prototype.compare = function(o){
 var ok = Object.keys(this);
 return typeof o === "object" && ok.length === Object.keys(o).length ? ok.every(k => this[k] === o[k]) : false;
};
Array.prototype.compare = function(a){
 return this.every((e,i) => typeof a[i] === "object" ? a[i].compare(e) : a[i] === e);
};
var fruits1 = [{"apple":25},{"bannana":36},{"orange":6}],
 fruits2 = [{"apple":25},{"bannana":36},{"orange":6}];
console.log(fruits1.compare(fruits2));

Answer 2

Simple function without library:

var arr1 = [1,2,3];
var arr2 = [1,2,4];
//This function takes one item, the index of the item, and another array to compare the item with.
function compare(item, index, array2){
 return array2[index] == item;
}
// the forEach method gives the item as first parameter
// the index as second parameter
// and the array as third parameter. All are optional.
arr1.forEach(function(item, index){
 console.log(compare(item, index, arr2));
});

Combine this with the answer Abdennour TOUMI gave, and you have an object comparison method :)

For simple objects you could use JSON.stringify(obj1) === JSON.stringify(obj2).

More info on object comparison can be found in this answer

Answer 3

Use underscore array functions. I would go with intersection

http://underscorejs.org/#intersection

Answer 4

You can use the following static method for Object class : Object.equals

Object.equals=function(a,b){if(a===b)return!0;if(!(a instanceof Object&&b instanceof Object))return!1;if(a.valueOf()===b.valueOf())return!0;if(a.constructor!==b.constructor)return!1;for(var c in a)if(a.hasOwnProperty(c)){if(!b.hasOwnProperty(c))return!1;if(a[c]!==b[c]){if("object"!=typeof a[c])return!1;if(!Object.equals(a[c],b[c]))return!1}}for(c in b)if(b.hasOwnProperty(c)&&!a.hasOwnProperty(c))return!1;return!0};
console.log(
 `"[1,2,3] == [1,2,3]" ?`,Object.equals([1,2,3],[1,2,3])
);
console.log(
 `"[{"apple":25},{"bannana":36},{"orange":6}] == [{"apple":25},{"bannana":36},{"orange":6}]" ?`,Object.equals([{"apple":25},{"bannana":36},{"orange":6}], [{"apple":25},{"bannana":36},{"orange":6}])
);