Javascript iterate objects in array only after current object

Question

For example:

From

[x0,x1,x2,x3] - x0 compares itself to x1,x2 and x3. 
x1 compares itself to x0, x2 and x3. And so on...

To

[x0,x1,x2,x3] - x0 compares itself to x1,x2 and x3. 
x1 compares itself to x2 and x3 only. 
x2 only compares itself to x3. 
x3 does not need to do any comparison at all.

Essentially I'm looking to traverse an array one way only, with every element behind the current element ignored.

for (var i = 0; i < boids.length; i++) { 
//boids is an array containing elements "boid"


     var d = distSquared(this.position.x, this.position.y, boids[i].position.x, boids[i].position.y); 
       //get distance between current boid and all other boids in array. 
       //Looking to change this to get distance between current boid and all other boids infront of this element in the array.

     if (boids[i] == this) { //if the boid being compared is to its own self, skip it.
            continue;
        }
}

How would I go about implementing such a structure?

Welcome to SO! Just a pointer, I just see 1 for loop. Can you share how comparison is done. — Rajesh Dixit
– Rajesh Dixit, Commented Sep 24, 2016 at 7:07
so even this will be there in boids array. So just search index of this in array and initialise i accordingly. — Rajesh Dixit
– Rajesh Dixit, Commented Sep 24, 2016 at 7:54

Rajesh Dixit · Accepted Answer · 2016-09-24 07:11:35Z

1

What you are looking for is something like this:

var a = [1,2,3,4];

for(var i=0; i<a.length; i++){
  for(var j=i+1; j<a.length; j++){
    console.log(i,j)
  }
}

answered Sep 24, 2016 at 7:11

Rajesh Dixit

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Comments

guest271314 · Accepted Answer · 2016-09-24 07:18:38Z

0

You can use Array.prototype.filter() to exclude an element or elements from an array

var arr = [1,2,3,4,5];
for (var i = 0; i < arr.length; i++) {
  var curr = arr[i];
  var not = arr.filter(function(_, index) {
    return index != i
  });
  console.log(`curr:${curr}`);
  not.forEach(function(el) {
    console.log(`${curr} is not ${el}`)
  })
}

edited Sep 24, 2016 at 7:18

answered Sep 24, 2016 at 7:03

guest271314

1

1 Comment

Carrein Over a year ago

Thanks for the reply, but I'm not looking to remove the currently check element in the list, but rather all elements behind it. Essentially I'm looking to traverse an array one way only.

Redu · Accepted Answer · 2016-09-24 08:40:11Z

0

You might do like this. Shaping up how to compare is up to you.

var arr = [1,2,3,4,5],
 result = arr.map((e,i,a) => a.slice(i+1).map(n => e-n));
console.log(result);

answered Sep 24, 2016 at 8:40

Redu

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Comments

Carrein · Accepted Answer · 2016-09-24 09:06:48Z

0

I used Array.prototype.indexOf() to solved my issue.

var j = boids.indexOf(this);
//get index of current element i array.

if (j < boids.length) {
    // if the index is lower than the overall length of the array (e.g. check traverse the array to elements infront of the current element, ignoring those behind)

    //Perform calculations here

   j++; //increment j

}

answered Sep 24, 2016 at 9:06

Carrein

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