Node.js, MongoDB, and AngularJS Web Development

Grouping Results

When performing operations on large data sets, it is often useful to group the results based on the distinct values of one or more fields in a document. You could do this in code after retrieving the documents, but it is much more efficient to have MongoDB do it for you as part of a single request that is already iterating though the documents.

To group the results of a query together, you can use the group() method on the Collection object. The group() request first collects all the documents that match a query and then adds a group object to an array, based on distinct values of a set of keys, performs operations on the group objects, and returns the array of group objects. The syntax for the group() methods is shown below: ...