Removing duplicate values from two arrays

Question

existing ["562fae5a626ca2e032947baa"] new array [ { _id: '562fae5a626ca2e032947baa' }, { _id: '562fae57626ca2e032947ba9' } ] modified [ { _id: '562fae5a626ca2e032947baa' }, { _id: '562fae57626ca2e032947ba9' } ]

I have an existing array and a new array, i want to compare the existing and the new array and remove the duplicates.

var existing = ["562fae5a626ca2e032947baa"]; var newArr = [ { _id: '562fae5a626ca2e032947baa' }, { _id: '562fae57626ca2e032947ba9' } ]; newArr = newArr.filter(function(val){ return existing.indexOf(val) == -1; }); console.log(newArr);

When i try to print newArr, i still get the two objects?

modified [ { _id: '562fae5a626ca2e032947baa' }, { _id: '562fae57626ca2e032947ba9' } ]

I want the modified array to have only.

modified [{ _id: '562fae57626ca2e032947ba9' } ]

Below is the fiddle. http://jsfiddle.net/ema6upg1/2/

You're trying to compare the simple string that's in existing to the objects that are in newArr. — Pointy
– Pointy, Commented Oct 27, 2015 at 17:13
Are those ids unique for existing? If so, use an object and save yourself some complexity. — James
– James, Commented Oct 27, 2015 at 17:36

Saransh Kataria · Accepted Answer · 2015-10-27 17:15:43Z

 newArr.filter(function(val){ return existing.indexOf(val._id) == -1; })

is what you need, val is an object, you need to compare its _id

Watte · Accepted Answer · 2015-10-27 17:16:18Z

Your problem is, that one array contains objects.

var existing = ["562fae5a626ca2e032947baa"]; var newArr = [ { _id: '562fae5a626ca2e032947baa' }, { _id: '562fae57626ca2e032947ba9' } ]; newArr = newArr.filter(function(val){ if(typeof val == "object") { return existing.indexOf(val._id) == -1; } return existing.indexOf(val) == -1; }); console.log(newArr);

James · Accepted Answer · 2015-10-27 17:38:13Z

The lookup for an object property is more efficient than iterating an array to find an id. Consider:

var existing = { "562fae5a626ca2e032947baa": true }; var newArr = [ { _id: '562fae5a626ca2e032947baa' }, { _id: '562fae57626ca2e032947ba9' } ]; newArr.filter(function(val) { return existing[val._id] || false; }

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