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?

You want to compare and then? You want to convert that array into an array of booleans? — acdcjunior, Mar 19 '18 at 16:37
if condition matches , needs to push new value (say 'maches' : true) for both the objects — fekky Dev, Mar 19 '18 at 16:40
Possible duplicate of [Lodash / javascript : Compare two collections and return the differences](https://stackoverflow.com/questions/40656124/lodash-javascript-compare-two-collections-and-return-the-differences) — Heretic Monkey, Mar 19 '18 at 16:44
I think by `x==y and y == x` he means `item1.x == item2.y and item1.y == item2.x`. — acdcjunior, Mar 19 '18 at 16:50

acdcjunior · Accepted Answer · 2018-03-19T17:02:00.483

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/lodash@4.17.5/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).

can you please explain me shortly – fekky Dev Mar 19 '18 at 16:55 — fekky Dev, Mar 19 '18 at 16:55
Added explanation. Check the answer, please – acdcjunior Mar 19 '18 at 17:05 — acdcjunior, Mar 19 '18 at 17:05

score 0 · Answer 2 · answered Mar 19 '18 at 16:37

0

var newArray = _.map(objects, function(item) {
    if (item.x == item.y) return item;
});

var filteredNewArray = _.without(newArray, undefined)

console.log(filteredNewArray)

answered Mar 19 '18 at 16:37

Sagar Jajoriya

2,377
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While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value. – Fraser Mar 19 '18 at 18:10
1

@Fraser, remember next time sure :) – Sagar Jajoriya Mar 19 '18 at 18:12

score 0 · Answer 3 · answered Mar 19 '18 at 16:41

0

You can use map. This may help,

objects.map((value, index) => {
    return value.x == value.y
})

answered Mar 19 '18 at 16:41

Reck

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

3 Answers3

Breakdown: