Node.js, MongoDB, and AngularJS Web Development

Aggregation Examples

Listing 15.9 shows how to implement aggregation against the words collection. It includes three examples.

The first example, in lines 10–20, implements a $match to get words beginning in vowels, then a $group to calculate the largest and smallest sizes. It then sorts the results using $sort, as shown in Figure 15.9.

Figure 15.9 Grouping documents from a MongoDB collection by specific field values.

The second example, in lines 21–27, uses $match to limit the words to four letters. Then $limit is used to process only five documents in the $project operator.

The third example, in lines 28–34, uses $group to get the average size ...