Testing for an array within an array

[Shaz]

I have an array where each element is an array of an x, y pair:

this.myArray: Array[2] 0: Array[2] 0: 1 1: 13 1: Array[2] 0: 2 1: 13I am trying to see if an x, y pair is contained in the array:

... = function(x, y) { return this.myArray.indexOf([x,y]) !== -1;}but this.myArray.indexOf([x,y]) is always equal to -1.

My JS book says indexOf uses a === equality tester. So I'm guessing it's just something to do with [1,2] === [1,2] not being true?

I will try this out:

... = function(x, y) {  return this.myArray.some(function(key) { return key[0] === x && key[1] === y }.bind(this));}

and use it if it works, but I'd really like to know why the original doesn't?

 

[Sulsay]

In javascript,

[1] === [1]will always return false. This is because arrays (and objects) are compared by reference, not by value. Both arrays point to a different location in memory.For scalars, such as integer 1, or string 'someString', the comparison is value-based, and thus

1 === 1will return true.If you were to do something like this, the result would be true because both variables reference the same array:

var x = [1];var y = x;var equal = x === y; // true

Your best option to check for equality is indeed to check the values in a loop. I think you're looking for every instead of some?

 

[Quxios]

The 1st case would only work if you check it with the same variable.

var test = [1, 2];var test2 = [test];test2.contains(test); // true because we used the object we put in the arraytest2.contains([1, 2]); // false because it creates a new objectI've come across this problems a few times. One way to get around it is to store in a string of the points instead of an array. Another is to store a variable that's unique to every point, I don't recall the name for this but the formulas:

i = x + y * maxwidth;which is what I ended up using.

 

[Shaz]

Thanks.


Using myArray.some did the trick. I only want to know if ANY array element has the same values, not if every one of them has.

 

[Helladen]

=== doesn't convert the data types to the same type when comparing, == does. 

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness

This doesn't really answer the question you are seeking, but it does give more insight about the comparison you are doing.

 

[Sulsay]

Then some() is indeed fine. Maybe you can simplify the check to something like this:

var array1 = [1, 2, 3],    array2 = [3, 4, 5];	var oneValueMatches = array1.some(function (value) { return array2.contains(value); })

 

[Shaz]

I think you are missing what I am trying to do. Array1's elements are arrays themselves, each of length 2. And I want to see if a specific array of length 2 is present in Array1. I am comparing arrays, not individual values.


I've already got it working, so the following is only by way of explanation.


Array1 contains a list of x/y coordinates that meet my conditions.


Array1:


0: [1,1]


1: [1,2]


2: [1,3]


3: [2,2]


I want to see if the coordinate x, y is contained in that list. So if [x,y] is [1,2] it would return true; if [x,y] is [2,1] it would return false.


contains would have worked in Ruby, but its implement in the core scripts use indexOf, which takes me back to where I was.


Anyway, I've got it working, so thanks for the input everyone.

 

[Sulsay]

You're right, I missed that. Glad you got it working! ;-)