Javascript Remove Item from array 1 if value exists in array 2

Question

Array 1

[ { "id": 1, "name": "Test" }, { "id": 2, "name": "Test2" } ]

Array 2

[ { "id": 1, "name": "Test3" }, { "id": 2, "name": "Test4" }, { "id": 3, "name": "Test2" } ]

If item exists in Array 2, I need to remove it from Array 1, so Test2 would be removed from Array 1. How can I loop through both arrays and check the name value's presence in Array 2 in order to remove it from Array 1?

• Felix Kling: Do you have a specific question about this? Why is the element with ID 1 not removed?
• gen_Eric: So, you are comparing by name, not id?
• gen_Eric: You should be able to use array_filter for this.
• Barmar: Convert Array 2 to an object that uses the IDs as property names. Then loop through Array 1, removing the elements that can't be found in the object.
• Barmar: @RocketHazmat That's PHP. You mean Array.prototype.filter.

Answer 1

I'm a big fan of underscorejs for this kind of thing...

array1 = _.reject(array1, function(e1) {
 return _.find(array2, function(e2) { return e1.name == e2.name });
});

Answer 2

Try this:

var existingIds = array2.map(function (item) { // create a list of existing ids in array 2
 return item.id;
 });
var filteredArray = array1.filter(function (item) { // check each item against existingIds, and if not found there return it
 return existingIds.indexOf(item.id) === -1;
 });

Answer 3

To do this without doing an O(n^2) search, we can do it looping once on each array, with a little extra memory overhead.

var map = new Map();
array2.forEach(function(item) {
 map.set(item.name, true);
});
var result = array1.filter(function(item) {
 return !map.has(item.name);
});

Note: I used Map simply because it has additional features, such as setting keys based on any value. A simple object can be used.