I've two arrays and I need to check they are not equal by their content (property by property)
Arrays and their current values are debugged in image.
Suggest any loadash function or javascript function to check deep equality which will exclude $$hashkey of array
Instead of lodash or javascript, there's method in angularjs to check equality of two objects: angular.equals & can be used as follows:
angular.equals(newValue, oldValue);
As it's angular's own equality check it doesn't have problem with $$hashkey it'll handle that (by not checking). Also it'll check equality by all property by property values with type checking also.
Plunker Example
You can use the _.isEqual function from Lodash. This function will compare all properties of your objects in your array.
var obj = [{ 'a': 1, b: 2 },{ 'a': 3, b: 4 }];
var other = [{ 'a': 1, b: 2 }, { 'a': 3, b: 4 }];
_.isEqual(obj, other); // => true
It's important to notice that the elements of both arrays need to be in the same order. This will return false:
var obj = [{ 'a': 1, b: 2 },{ 'a': 3, b: 4 }];
var other = [{ 'a': 3, b: 4 },{ 'a': 1, b: 2 }];
_.isEqual(obj, other); // => false
UPDATE
With _.isEqual you need the have two arrays in the same order. But to overcome this orderly comparison, you can use other lodash function, so in your case you can use like this (using sortBy):
_.isEqual(_.sortBy(obj, 'id'), _.sortBy(other, 'id'));
This will first sort the arrays by id and after verify if the arrays are equal. You can sort by multiple properties too, or by a custom function.
Related
This question already has answers here:
How to compare arrays in JavaScript?
(61 answers)
Why are two identical objects not equal to each other?
(9 answers)
Closed 2 years ago.
I started with:
"1:2".split(':') == ["1","2"];
// false
Then tried:
[1,2] == [1,2];
// false
and ultimately:
[] == [];
// false
I've since found that:
"1:2".split(':').toString() == [1,2].toString();
// true
So I've solved my initial issue (kind of) but why can't arrays match each other?
Javascript arrays are objects and you can't simply use the equality operator == to understand if the content of those objects is the same. The equality operator will only test if two object are actually exactly the same instance (e.g. myObjVariable==myObjVariable, works for null and undefined too).
If you need to check if two array are equals i'd recommend to just traverse both arrays and verify that all the elements have the same value (and that the two array have the same length).
Regarding custom objects equality i'd build instead a specific equals function and i'd add it to the prototype of your class.
Considering that in the end you converted both arrays to a String and tested equality of the resulting strings, you could one day consider using a similar but more generic technique you'll find described in more than a few places:
JSON.stringify(OBJ1) === JSON.stringify(OBJ2)
Well, don't.
While this could work if the order of the properties will always the same for those object instances, this leaves the door open for extremely nasty bugs that could be hard to track down. Always favor a more explicit approach and just write a clean and readable function that will test for equality checking all the required fields.
The == operator for Objects in Javascript only checks to see if the objects are the same actual object reference, not if they are two separate object that contain the same contents. There is no built in operator for checking if they contain the same contents. You would have to write a function to do that sort of comparison yourself.
Your string conversion is one way of comparing two arrays as long as the array elements only contain primitive values (not other objects). If the array elements could contain other elements, then you would have to make sure those objects were themselves converted into representative strings too.
And, converting to a string would not discern between an array element that contains "4" versus one that contains 4 since both convert to "4" in the string representation.
FYI, you can read in this answer about records and tuples, two new data types coming to future Javascript that will allow comparing an immutable version of arrays and objects by value instead of by only comparing to see if they are the same object.
Equality for objects will tell you if the two objects are the same one.
var a = [];
var b = a;
a === b; // True, a and b refer to the same object
[] === []; // False, two separate objects
You will have to loop through the arrays to see if they have the same elements.
See: How to check if two arrays are equal with JavaScript?
In javascript each [] is an instance of window.Array class. So you are basically trying to compare two different objects. Since array's can have any no. and any type of elements including Objects and Custom Objects and those nested arrays can again have numerous properties and arrays and so on.
It becomes ambiguous when it comes to comparison, you will never be sure what do you want to do with those objects and nested properties. So what you are trying to achieve by comparing can be done in so many other ways. You just have to figure out the right way for your case.
One way is to make your own Array checking function:
How to compare arrays in JavaScript?!
Another way is to convert the Array to a String with .join(), and compare the strings. Then convert them back into Arrays with .split().
If I relate this problem with that in Python:
Input:
a="1 2 3 4"
case I:
a=input.split(' ')
output: ['1', '2', '3', '4']
case II:
a=map(int,input.split(' '))
output: [1, 2, 3, 4]
So, the fault is that of type, as it could come-out aa 'true' for:
"1:2".split(':').toString() == [1,2].toString(); //true
This question already has answers here:
How to compare arrays in JavaScript?
(61 answers)
Why are two identical objects not equal to each other?
(9 answers)
Closed 2 years ago.
I started with:
"1:2".split(':') == ["1","2"];
// false
Then tried:
[1,2] == [1,2];
// false
and ultimately:
[] == [];
// false
I've since found that:
"1:2".split(':').toString() == [1,2].toString();
// true
So I've solved my initial issue (kind of) but why can't arrays match each other?
Javascript arrays are objects and you can't simply use the equality operator == to understand if the content of those objects is the same. The equality operator will only test if two object are actually exactly the same instance (e.g. myObjVariable==myObjVariable, works for null and undefined too).
If you need to check if two array are equals i'd recommend to just traverse both arrays and verify that all the elements have the same value (and that the two array have the same length).
Regarding custom objects equality i'd build instead a specific equals function and i'd add it to the prototype of your class.
Considering that in the end you converted both arrays to a String and tested equality of the resulting strings, you could one day consider using a similar but more generic technique you'll find described in more than a few places:
JSON.stringify(OBJ1) === JSON.stringify(OBJ2)
Well, don't.
While this could work if the order of the properties will always the same for those object instances, this leaves the door open for extremely nasty bugs that could be hard to track down. Always favor a more explicit approach and just write a clean and readable function that will test for equality checking all the required fields.
The == operator for Objects in Javascript only checks to see if the objects are the same actual object reference, not if they are two separate object that contain the same contents. There is no built in operator for checking if they contain the same contents. You would have to write a function to do that sort of comparison yourself.
Your string conversion is one way of comparing two arrays as long as the array elements only contain primitive values (not other objects). If the array elements could contain other elements, then you would have to make sure those objects were themselves converted into representative strings too.
And, converting to a string would not discern between an array element that contains "4" versus one that contains 4 since both convert to "4" in the string representation.
FYI, you can read in this answer about records and tuples, two new data types coming to future Javascript that will allow comparing an immutable version of arrays and objects by value instead of by only comparing to see if they are the same object.
Equality for objects will tell you if the two objects are the same one.
var a = [];
var b = a;
a === b; // True, a and b refer to the same object
[] === []; // False, two separate objects
You will have to loop through the arrays to see if they have the same elements.
See: How to check if two arrays are equal with JavaScript?
In javascript each [] is an instance of window.Array class. So you are basically trying to compare two different objects. Since array's can have any no. and any type of elements including Objects and Custom Objects and those nested arrays can again have numerous properties and arrays and so on.
It becomes ambiguous when it comes to comparison, you will never be sure what do you want to do with those objects and nested properties. So what you are trying to achieve by comparing can be done in so many other ways. You just have to figure out the right way for your case.
One way is to make your own Array checking function:
How to compare arrays in JavaScript?!
Another way is to convert the Array to a String with .join(), and compare the strings. Then convert them back into Arrays with .split().
If I relate this problem with that in Python:
Input:
a="1 2 3 4"
case I:
a=input.split(' ')
output: ['1', '2', '3', '4']
case II:
a=map(int,input.split(' '))
output: [1, 2, 3, 4]
So, the fault is that of type, as it could come-out aa 'true' for:
"1:2".split(':').toString() == [1,2].toString(); //true
Let I have a JavaScript object like the following: {a: 'a', b: 'b' , c: 'c'}. I want ot return an object which consist of the properties satisfies, for instance a\bregexp. Is it possible to do in JavaScript?
Javascript doesn't have a function for this, however it is possible if you loop over the keys yourself, using for (key in array) {}. Then you can apply the regex to each key seperately and retrieve the corresponding value if it matches.
Since typed arrays are just normal Arrays with typed values, they should also be considered "Arrays". But when I test if typed arrays are arrays, it returns false. For example:
var arr = new Int32Array(3);
Array.isArray(arr); //false
Does Array.isArray only check if arr is exactly a type Array object? How can I test if arr is an array, regardless of typed or not typed?
Typed Arrays are very different beasts than arrays. Arrays are generic collections, with loads of helper-methods for operating on those collections.
Typed Arrays were put in primarily to help with the browser version of OpenGL (though they obviously have other uses).
Try calling typedInt8Array.forEach()...
They're not the same thing.
So if you want a function which checks whether a variable/property is an array, or a typed array, then you will have to manually check the instanceof for each of the Int8Array|Int16Array|etc....
I'm partial to this trick:
obj.length === +obj.length; // true if it's an array
Since JavaScript Arrays have the special length property this is a pretty safe way to tell unless you have objects that you've defined a length property on manually.
Since Typed Arrays still have a length property, the old trick
obj.length === +obj.length
still works.
That means that length is a numeric property ( +v transforms a var to number, so if it's still === after the transform, then it was a number to begin with).
This is a solution I came up with:
isArray = /Array/.test(arr.constructor.name);
Any programming language which provides arrays (lists, vectors, tuples etc.) must decide whether they have reference or value semantics, with the usual/obvious choice being reference semantics for mutable arrays and value semantics for immutable ones.
JavaScript which provides mutable arrays appears to have chosen reference semantics e.g. given
var a = [1, 2, 3]
var b = [1, 2, 3]
then a != b, as expected because though they have the same contents, they are different arrays.
However when you use them as keys in an object, the picture changes; if you set obj[a] to a value, then obj[b] gets the same value. Furthermore, this remains true if you change the contents of the arrays; at least when I tested it in Rhino, it behaves as though the interpreter were recursively comparing the full contents of the supplied and stored key arrays on every lookup, complete with a check for the infinite loop that would occur if one of the arrays were made to point to itself.
Is this the intended/specified behavior in all implementations?
Does it also apply to objects used as keys?
Is there any way to get the other behavior, i.e. to look up values using arrays as keys with reference semantics?
When arrays are used as property names they are cast to a string:
[1,2,3].toString() == '1,2,3'
Once turned into a string value, arrays with the same contents would map to the same property.
To answer your last question, you can't use objects to reference property names (keys) whereby only the same object maps to the same property (1:1 mapping).
obj[a] and obj[b] will run the toString function on the arrays and produce the same result for both. It doesn't try to use the arrays as keys.
var a = [1,2,3];
var x = {};
x[a] = "test";
var i;
for(i in x)
{
alert(i); //"1,2,3"
}
jsFiddle example