Distinct list of values
A common requirement in the user interface of an application is to provide a drop-down picklist of possible values in an input field of a form ready for the application user to select one of the values. Here, you will learn how to populate a list of unique values ready for use in a drop-down widget.
Scenario
You want to query a collection of people where each document contains data on one or more languages spoken by the person. The query result should be an alphabetically sorted list of unique languages that a developer can subsequently use to populate a list of values in a user interface's drop-down widget.
This example is the equivalent of a SELECT DISTINCT statement in SQL.
Populating the sample data
Drop any old versions of the database (if they exist) and then populate a new persons collection. Each person document includes the person's first name, last name, vocation, and spoken languages:
db = db.getSiblingDB("book-distinct...
