How can i get arrays intersection include duplicate values using Javascript

Question

I need something like lodash.intersectionWith but I also need duplicated values in result array.

Example:

var objects = [{ 'x': 1, 'y': 2 }, { 'x': 2, 'y': 1 }, { 'x': 1, 'y': 2 }];
var others = [{ 'x': 1, 'y': 1 }, { 'x': 1, 'y': 2 }];
_.intersectionWith(objects, others, _.isEqual);

Expected Result:

[{ 'x': 1, 'y': 2 },{ 'x': 1, 'y': 2 }]

Thanks in advance!

It's not exactly clear why you expect there to be 2 copies of that object and not 3. — Omri Aharon
– Omri Aharon, Commented May 25, 2016 at 10:22

1983 · Accepted Answer · 2016-05-25 13:02:29Z

3

You can find the intersection by filtering out items from the first array that don't match items in the second. Any duplicates in the first array will be kept.

var intersectwith = function(f,xs,ys){
    return xs.filter(function(x){
        return ys.some(function(y){
            return f(x,y);
        });
    });
};

var equals = function(x,y){
    return x === y;
};
console.log(intersectwith(equals, [1,2,3], [1,1,2,2,4]));
console.log(intersectwith(equals, [1,1,2,2,4], [1,2,3]));

Or, more readably, using ES6:

const intersectwith = (f,xs,ys) => xs.filter(x => ys.some(y => f(x,y)));
const equals = (x,y) => x === y;

console.log(intersectwith(equals, [1,2,3], [1,1,2,2,4]));
console.log(intersectwith(equals, [1,1,2,2,4], [1,2,3]));

Substitute _.isEqual for equals for comparing objects: jsfiddle.

Useful documentation:
Array.prototype.filter
Array.prototype.some

edited May 25, 2016 at 13:02

answered May 25, 2016 at 10:47

1983

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2 Comments

1983 Over a year ago

You can use a different comparison function, e.g. _.isEqual. I wanted to show it working in the code snippet.

1983 Over a year ago

Edited to add jsfiddle showing it in action with objects.

ryeballar · Accepted Answer · 2016-05-25 12:01:14Z

3

You can make use of differenceWith() to get the difference between the source object and the symmetric difference of the source object and the others object using xorWith().

var result = _.differenceWith(
  objects, 
  _.xorWith(objects, others, _.isEqual), 
  _.isEqual
);

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


var intersection = _.intersectionWith(objects, others, _.isEqual);

var result = _.differenceWith(
  objects, 
  _.xorWith(objects, others, _.isEqual), 
  _.isEqual
);

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.13.1/lodash.js"></script>

edited May 25, 2016 at 12:01

answered May 25, 2016 at 10:52

ryeballar

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6 Comments

Mikhail Over a year ago

I like this approach, but here is one problem, my actual arrays have different object types 'objects are Jquery' and 'others are javascript object'. The problem is that xorWith()'s comparator function at some point switches arguments (have no idea why).

ryeballar Over a year ago

@Mikhail please check my update, I changed difference() to differenceWith().

Mikhail Over a year ago

intersectionWith() works fine. I made a test you can check it out.

ryeballar Over a year ago

I can see that in your test, the source object does only contain the x and y property. You should have added such statement. And your test definitely failed. If you log the intersection result it would return an empty array.

Mikhail Over a year ago

I update demo. But any way it is just to see the difference between Xor and Intersection comparator functions.

|

Randy · Accepted Answer · 2016-05-25 10:39:43Z

0

Use reduce to validate each object in the first array, then check if that object exists in the second array. If it exists, reduce will push that object into its array.

The reduce function will return that new array automagically.

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

var res = objects.reduce(
  function(arr, obj){
    if(containsObject(obj, others))
      arr.push(obj);
    return arr;
  }, 
  []
);


function containsObject(obj, list) {
    var x;
    var ret = false;
  
    list.forEach(function(s){
      ret = JSON.stringify(s) == JSON.stringify(obj);
    });

    return ret;
}

console.log(res);

edited May 25, 2016 at 10:39

answered May 25, 2016 at 10:33

Randy

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