Calculating match percentage using new aggregation pipeline set operators

[Tam Do]

Hi,

I am working on a search algorithm implemented using the mongo aggregation pipeline.  I have essentially two sets:

Set A contains a list of unique items e.g., ['A', 'B', 'C', 'D', 'E', 'F', 'G']

Set B contains a unique list of items which may or may be present in Set A e.g., ['C', 'B', 'G', 'H', 'J', 'K']

Using the $setIntersection operator I can find a list of elements common to sets A and B

{$project : { C : { $setIntersection : [A, B] } }

Which should result in C : ['C', 'B']

What I would like to do is take the count of C and divide it by the length of A

percent_match = len(A) / len(C)

and return results which are greater than a defined threshold.

Is this possible with the aggregation pipeline? If so, I could use some pointers in terms of operators and structure of the pipeline.

Thanks!

--Tam Do

[Asya Kamsky]

You can use the $size operator (new in 2.6) to project size of array and use $divide and $multiply to calculate percentage from that.

Asya

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