Comparison of array of objects in the same collection with similar properties

Question

I'm trying to compare each object in the array.

Let's say below is my array:

var objects = [{
        'x': 1,
        'y': 2
    }, {
        'x': 2,
        'y': 1
    },{
        'x': 3,
        'y': 1
    },{
        'x': 4,
        'y': 1
    }];

Given two items, say item1 and item2, I need to check the condition item1.x == item2.y and item1.y == item2.x through the array.

Is there a clean/efficient way to do in Lodash?

Answer 1

var objects = [
    {'x': 1, 'y': 2},
    {'x': 2, 'y': 1},
    {'x': 3, 'y': 1},
    {'x': 4, 'y': 1}
];
    
var comparedLodash = _.map(objects, function (item) {
  return !!_.find(objects, {x: item.y, y: item.x}); 
});
console.log(comparedLodash);

<script src="https://cdn.jsdelivr.net/npm/[email protected]/lodash.min.js"></script>

Complexity of this is O(n^2).

_{Note: You could make it O(nlogn) if you sorted the array before starting the comparison, but this would add significant noise to the code.}

Breakdown:

The _.map(somearray, somefunction) function executes the somefunction into every element of somearray. We will use it to convert every item of the objects array into a boolean. Roughly it is like:

var comparedLodash = _.map(objects, functionThatWillConvertAnItemIntoABoolean);

Now, each item1 should be converted true if there's anotherItem with item1.x == anotherItem.y and item1.y == anotherItem.x. To find if this another item exists, we use _.find().

_.find(somearray, someobject) tries to if the someobject exists in the somearray. That is why we do, above, something like:

function (item) {
  var anotherItem = {x: item.y, y: item.x}
  return _.find(objects, anotherItem); 
}

Lastly, _.find returns the object, if found, and undefined if not found. We use !! to convert that to boolean (!!undefined becomes false and !!someobject becomes true).