collection.group

Mongo documentation

Run a group command across a collection.

Arguments

1. keys (object | array | function) - An object, array or function expressing the keys to group by.

2. condition (Object) - An optional condition that must be true for a row to be considered.

3. initial (Object) - Initial value of the aggregation counter object.

4. reduce (Function) - The reduce function aggregates (reduces) the objects iterated.

5. [finalize] (Function) - An optional function to be run on each item in the result set just before the item is returned.

6. [command] (Boolean) - Specify if you wish to run using the internal group command or using eval, default is true.

7. [options] (Object)

8. [callback] (function)

Returns

A promise.

Example

users.group(
  { a: true },
  {},
  { count: 0 },
  function (obj, prev) {
    prev.count++
  },
  true
)