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Lez Yeoh February 2016

Difference between two arrays of Mongo Document _ids

Essentially, I have two arrays of _ids from Mongodb that I'm trying to compare/get the differences of.

Array 1 comes directly from a document.find() call. Array 2 comes from an document.Aggregate call, of which I then _.pluck the _id from both of them.

Array 1 might look like [ 1 , 57, 58, 100 ] as an example.
Array 2 might look like [ 1 , 2, 3, 4, 55, 100 ] as an example.

I want to find the difference and return and [ 57, 58 ].

To do this I've been using lodash as the library. And I've tried the following two methods:

_.difference(array1, array2)


_.filter(array1, function(obj){ return !_.findWhere(array2, obj); });

But both don't seem to work. I'd love some help if possible.


Lez Yeoh February 2016

Ignore. Turns out the filter code worked. It was my db with the error.

_.filter(array1, function(obj){ return !_.findWhere(array2, obj); });

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Asked in February 2016
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