Get the count of items in subcategories

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There is a tree of categories, such as

Mammalia-Rodentia...,
...,
Mammalia-Primates-Hominidae...,
Mammalia-Primates-Lemuridae...,
...
etc.

There is a set of categorized beings.

Given a category (e.g. Mammalia or Primates) how to calculate the number of beings in each subcategory:

{ Primates: 1098, Rodentia: 8932 }

or

{ Lemuridae: 129, Hominidae: 432 }

I'm trying to model Beings like this:

{
   name: "being #1",
   categories: [...,'Lemuridae', 'Primates', 'Mammalia']
}

To aggregate for e.g. Primates I {$match : {categories:'Primates'}} then I nees $project a category just before 'Primates' and it looks like this is impossible within aggregation framework... Thus either the model is incorrect or I have to use mapreduce...

Any Ideas?

asked 37 secs ago

Andrei Toutoukine

1

Get the count of items in subcategories